Etymology dictionary

then (adv.) — think tank (n.)

then (adv.)

adverb of time, Old English þanne, þænne, þonne, from Proto-Germanic *thana- (source also of Old Frisian thenne, Old Saxon thanna, Dutch dan, Old High German danne, German dann), from PIE demonstrative pronoun root *to- (see the).

As a conjunction, "in that case, therefore," in Old English. As an adjective, "being at that time," from 1580s. As a noun from early 14c. For further sense development, see than. Similar evolutions in other Germanic languages; Dutch uses dan in both senses, but German has dann (adv.) "then," denn (conj.) "than." Now and then "at various times" is attested from 1550s; earlier then and then (c. 1200).

thence (adv.)

late 13c., from Old English þanone, þanon "from that place" + adverbial genitive -es. Old English þanone/þanon is from Proto-Germanic *thanana (source also of Old Saxon thanana, Old Norse þana, Old Frisian thana, Old High German danana, German von dannen), related obscurely to the root of then, and ultimately from PIE demonstrative base *to- (see the). Written with -c- to indicate a voiceless "s" sound. Meaning "from that time" is from late 14c.; sense of "for that reason" is from 1650s. From thence is redundant.

thenceforth (adv.)

late 14c., from thence + forth.

thenceforward (adv.)

mid-15c., from thence + forward.

theo-

word-forming element meaning "god, gods, God," from Greek theos "god," from PIE root *dhes-, forming words for religious concepts, such as Latin feriae "holidays," festus "festive," fanum "temple."

Theobald

masc. proper name, from Medieval Latin Theobaldus, from Old High German Theudobald, from theuda "folk, people" (see Teutonic) + bald "bold" (see bold). Form influenced in Medieval Latin by the many Greek-derived names beginning in Theo-.

theocentric (adj.)

1856, from theo- + -centric.

theocracy (n.)

1737; earlier as un-Latinized theocraty (1620s), "form of government in which God is recognized as supreme ruler and his laws form the statute book," originally of the sacerdotal government of Israel before the rise of kings, from later Greek theokratia (Josephus), literally "the rule of God," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + kratos "a rule, regime, strength" (see -cracy). Meaning "priestly or religious body wielding political and civil power" is recorded from 1825. Related: Theocratic (1741).

theocrat (n.)

1827, "a ruler in the name of God," from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + -crat, from aristocrat, etc. From 1843 as "one who favors a system of theocracy." Theocratist was the name of a publication begun in 1828 "to maintain the essential relation which subsists between religion and politics," and might be used in the sense "one who emphasizes divine authority over reason and individual freedom and who explains social order as a revelation from God."

theodicy (n.)

"vindication of divine justice," 1771, from French théodicée, title of a 1710 work by Leibniz to prove the justice of God in a world with much moral and physical evil, from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + dikē "custom, usage; justice, right; court case" (see Eurydice). Related: Theodicean.

theodolite (n.)

surveying instrument, 1570s, of unknown origin (see OED for discussion). "The word has a Gr[eek] semblance, but no obvious Gr[eek] basis" [Century Dictionary].

Theodore

masc. proper name, from Latin Theodorus, from Greek Theodoros, literally "gift of god," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + dōron "gift" (from PIE root *do- "to give"). The fem. form is Theodora.

Theodoric

masc. proper name, from Late Latin Theodoricus, from Gothic, literally "ruler of the people," from Gothic þiuda "people" (see Teutonic) + *reiks "ruler" (see Reich). For spelling, see Theobald. The French form of the name, via the Franks, is Thierry.

Theodosia

fem. proper name, from Greek Theodosia, literally "gift of the gods," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + dosis "a giving," from stem of didonai "to give" (from PIE root *do- "to give").

theogony (n.)

1610s, "the account of the birth or genealogy of the gods," from Greek theogonia "generation or genealogy of the gods," from theos "a god" (from PIE root *dhes-, forming words for religious concepts) + -gonia "a begetting," from gonos "birth" (from PIE root *gene- "give birth, beget").

theological (adj.)

early 15c., "pertaining to theology," from Medieval Latin theologicalis, from Latin theologicus, from theologia (see theology). Related: Theologically.

theology (n.)

mid-14c., "the science of religion, study of God and his relationship to humanity," from Old French theologie "philosophical study of Christian doctrine; Scripture" (14c.), from Latin theologia, from Greek theologia "an account of the gods," from theologos "one discoursing on the gods," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + -logos "treating of" (see -logy). Meaning "a particular system of theology" is from 1660s.

theologian (n.)

late 15c., from Old French theologien (14c.), from theologie; see theology. A petty or paltry theologist is a theologaster (1620s), used in Medieval Latin by Martin Luther (1518).

theologist (n.)

1630s, from Medieval Latin theologista, agent noun from theologizare, from Latin theologia (see theology). Earlier in the same sense was theologician (1550s).

theophany (n.)

"an appearance of God to man," 1630s, from Late Latin theophania, from Greek theos "god" (from PIE root *dhes-, forming words for religious concepts) + phainein "bring to light, cause to appear, show" (from PIE root *bha- (1) "to shine"). In Middle English "Epiphany" (late 12c.). Ancient Greek Theophaneia was the name of a festival at Delphi during which the statues of Apollo and other gods were displayed to the public.

Theophilus

masc. proper name, Latinized form of Greek Theophilos, literally "dear to God; loved by the gods," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + philos "loved, beloved" (see -phile).

theorem (n.)

"demonstrable proposition in science or mathematics," 1550s, from French théorème (16c.) and directly from Late Latin theorema, from Greek theorema "spectacle, sight," in Euclid "proposition to be proved," literally "that which is looked at," from theorein "to look at, behold" (see theory).

theoretical (adj.)

1610s, "contemplative," with -al (1) + Late Latin theoreticus "of or pertaining to theory," from Greek theoretikos "contemplative, speculative, pertaining to theory" (by Aristotle contrasted to praktikos), from theoretos "that may be seen or considered," from theorein "to consider, look at" (see theory). Meaning "pertaining to theory, making deductions from theory not from fact" (opposed to practical) is from 1650s; earlier in this sense was theorical (c. 1500). Meaning "ideal, hypothetical" is from 1790s (implied in theoretically). Related: theoretician.

theory (n.)

1590s, "conception, mental scheme," from Late Latin theoria (Jerome), from Greek theōria "contemplation, speculation; a looking at, viewing; a sight, show, spectacle, things looked at," from theōrein "to consider, speculate, look at," from theōros "spectator," from thea "a view" (see theater) + horan "to see," which is possibly from PIE root *wer- (3) "to perceive." Philosophy credits sense evolution in the Greek word to Pythagoras.

Earlier in this sense was theorical (n.), late 15c. Sense of "principles or methods of a science or art" (rather than its practice) is first recorded 1610s (as in music theory, which is the science of musical composition, apart from practice or performance). Sense of "an intelligible explanation based on observation and reasoning" is from 1630s.

theorist (n.)

"one given to theory and speculation," 1590s; see theory + -ist.

theorize (v.)

1630s, perhaps a formation in English from theory + -ize. Related: Theorized; theorizing.

theosophy (n.)

1640s (implied in theosophical), "knowledge of divine things obtained through mystic study," from Medieval Latin theosophia (c.880), from Late Greek theosophia (c.500) "wisdom concerning God or things divine," from Greek theosophos "one wise about God," from theos "god" (from PIE root *dhes-, forming words for religious concepts) + sophia "skill, knowledge of, acquaintance with; philosophy," from sophos "wise, learned" (see sophist).

Applied variously over the years, including to the followers of Swedenborg. Taken as the name of a modern philosophical system (sometimes called Esoteric Buddhism), founded in New York 1875 as "Theosophical Society" by Madame Blavatsky and others, which has elements of Hinduism and Buddhism and claims supernatural knowledge of the divinity and his words deeper than that obtained from empiricism. Related: Theosophist.

ther-

often thero-, word-forming element meaning "beast," from Greek thēr "wild beast, beast of prey," from PIE root *ghwer- "wild beast." Also therio-, from Greek thērion "wild animal, hunted animal."

therapeutic (adj.)

pertaining to the healing of disease, 1640s, from Modern Latin therapeuticus "curing, healing," from Greek therapeutikos, from therapeutein "to cure, treat medically," primarily "do service, take care of, provide for," of unknown origin, related to therapon "attendant." Therapeutic was used from 1540s as a noun meaning "the branch of medicine concerned with treatment of disease." Related: Therapeutical (c. 1600).

therapy (n.)

1846, "the science of medical treatment of disease," from Modern Latin therapia, from Greek therapeia "curing, healing, service done to the sick; a waiting on, service," from therapeuein "to cure, treat medically," literally "attend, do service, take care of" (see therapeutic).

Middle English had it as terapeucia "therapeutics" (early 15c.) perhaps via Medieval Latin.

therapist (n.)

1880, from therapy + -ist; earlier was therapeutist (1816). Especially of psychotherapy practitioners from c. 1930s.

there (adv., conj.)

Old English þær "in or at that place, so far as, provided that, in that respect," from Proto-Germanic *thær (source also of Old Saxon thar, Old Frisian ther, Middle Low German dar, Middle Dutch daer, Dutch daar, Old High German dar, German da, Gothic þar, Old Norse þar), from PIE *tar- "there" (source also of Sanskrit tar-hi "then"), from root *to- (see the) + adverbial suffix -r.

Interjectional use is recorded from 1530s, used variously to emphasize certainty, encouragement, or consolation. To have been there "had previous experience of some activity" is recorded from 1877.

thereabouts (adv.)

early 15c., "in that area, around there; mid-15c., "near to that time, approximately thence," from Old English þær onbutan "about that place" + adverbial genitive -es; see there + about.

thereafter (adv.)

Old English þær æfter; see there + after. Similar formation in Dutch daarachter, Swedish derefter.

thereby (adv.)

Old English þærbig "thus, by means of or because of that;" see there + by. Similar formation in Old Frisian therbi, Middle Low German darbi, German dabei, Dutch daarbij.

therefore (adv.)

Old English þærfore; from there + fore, Old English and Middle English collateral form of for. Since c. 1800, therefor has been used in sense of "for that, by reason of that;" and therefore in sense of "in consequence of that." Similar formation in Dutch daarvoor, German dafür, Danish derfor.

therefor (adv.)

"for this, for that," Middle English variant spelling of therefore (q.v.); in modern use perhaps perceived as there + for.

therefrom (adv.)

mid-13c., there from. One word from 17c.; see there + from.

therein (adv.)

"in that place, time, or thing," Old English þærin; see there + in. Similar formation in German darin.

theremin (n.)

electronic musical instrument, 1927, from the name of its inventor, Russian engineer Léon Thérémin (1896-1993).

thereof (adv.)

"of that, of it," Old English þærof; see there + of. Similar formation in Swedish, Danish deraf.

thereon (adv.)

Old English þæron; see there + on. Similar formation in German daran.

Theresa

also Teresa, fem. proper name, from French Thérèse, from Latin Therasia, apparently from Greek Therasia, name of two volcanic islands, one near Sicily, one near Crete. In the top 50 most popular names for girls born in the U.S. from 1953 to 1969.

thereto (adv.)

Old English þærto "to it, in that place, for that purpose, belonging to;" see there + to. Similar formation in Old Saxon tharto, Old High German darazuo, German dazu.

thereunder (adv.)

Old English þærunder; see there + under. Similar formation in Old Frisian therunder, German darunter.

thereupon (adv.)

late 12c., þer uppon; see there + upon.

therewith (adv.)

c. 1200, "along with, in company with," from there + with. Old English þær wiþ meant "against, in exchange for." Similar formation in Swedish dervid, Danish derved.

thermal (adj.)

1756, "having to do with hot springs," from French thermal (Buffon), from Greek therme "heat, feverish heat" (from PIE root *gwher- "to heat, warm"). The sense of "having to do with heat" is recorded by 1837. The noun meaning "rising current of relatively warm air" is recorded from 1933.

Thermos (n.)

trademark registered in Britain 1907, invented by Sir James Dewar (patented 1904 but not named then), from Greek thermos "hot" (from PIE root *gwher- "to heat, warm"). Dewar built the first one in 1892, but it was first manufactured commercially in Germany in 1904, when two glass blowers formed Thermos GmbH. Supposedly the company sponsored a contest to name the thing, and a Munich resident won with a submission of Thermos.

thermo-

before vowels therm-, word-forming element meaning "hot, heat, temperature," used in scientific and technical words, from Greek thermos "hot, warm," therme "heat" (from PIE root *gwher- "to heat, warm").

thermochemistry (n.)

also thermo-chemistry, 1840, from thermo- + chemistry.

thermocline (n.)

1897, from thermo- + -cline, from Greek klinein "to slope," from PIE root *klei- "to lean."

thermocouple (n.)

also thermo-couple, 1862, from thermo-electric + couple (n.).

thermodynamic (adj.)

1849, from thermo- + dynamic (adj.).

thermodynamics (n.)

theory of relationship between heat and mechanical energy, 1854, from thermodynamic (adj.); also see -ics. "The consideration of moving forces, though suggested by the form of the word, does not enter into the subject to any considerable extent" [Century Dictionary].

thermograph (n.)

"automatic self-registering thermometer," 1881, from thermo- + -graph "instrument for recording; something written." Related: Thermographic.

thermography (n.)

1840, "method of writing which requires heat to develop the characters," from thermo- + -graphy.

thermometer (n.)

1630s, from French thermomètre (1620s), coined by Jesuit Father Jean Leuréchon from Greek thermos "hot" (see thermal) + metron "measure" (from PIE root *me- (2) "to measure"). An earlier, Latinate form was thermoscopium (1610s). The earliest such device was Galileo's air-thermometer, invented c. 1597. The typical modern version, with mercury in glass, was invented by Fahrenheit in 1714. Related: Thermometric; thermometrical.

thermonuclear (adj.)

1938 with reference to stars, 1953 of weapons (technically only to describe the hydrogen bomb), from thermo- + nuclear.

thermoplastic (adj.)

1870, see thermo- + plastic (adj.). As a noun from 1929.

Thermopylae

narrow land passage along the Malian Gulf in ancient Greece, from Greek thermos "hot" (from PIE root *gwher- "to heat, warm") + pylai, plural of pylē "gate; mountain pass, entrance into a region" (see pylon). In reference to nearby hot sulfur springs. Often simply hai pylai "the gates." Figurative of heroic resistance against overwhelming numbers since the battle fought there between the Greeks and Persians in 480 B.C.E.

thermosphere (n.)

1924, from thermo- + sphere.

thermostat (n.)

automatic instrument for regulating temperature, 1831, from thermo- + -stat.

Theropoda (n.)

order of dinosaurs, Modern Latin, from Greek elements: thēr "wild beast, beast of prey" (from PIE root *ghwer- "wild beast") + podos genitive of pous "foot" (from PIE root *ped- "foot"). So called because the structure of the feet resembled quadrupeds rather than birds. Related: Theropod.

thesaurus (n.)

1823, "treasury, storehouse," from Latin thesaurus "treasury, a hoard, a treasure, something laid up," figuratively "repository, collection," from Greek thēsauros "a treasure, treasury, storehouse, chest," related to tithenai "to put, to place." According to Watkins, it is from a reduplicated form of PIE root *dhe- "to set, put," but Beekes offers: "No etymology, but probably a technical loanword, without a doubt from Pre-Greek."

The meaning "encyclopedia filled with information" is from 1840, but existed earlier as thesaurarie (1590s), used as a title by early dictionary compilers, on the notion of thesaurus verborum "a treasury of words." Meaning "collection of words arranged according to sense" is first attested 1852 in Roget's title. Thesaurer is attested in Middle English for "treasurer" and thesaur "treasure" was in use 15c.-16c.

these (pron.)

Old English þæs, variant of þas (which became those and took the role of plural of that), nominative and accusative plural of þes, þeos, þis "this" (see this). Differentiation of these and those is from late 13c. OED begins its long entry with the warning, "This word has a complicated history."

Theseus

legendary hero-king of Athens; the name is of uncertain origin.

thesis (n.)

late 14c., "unaccented syllable or note," from Latin thesis "unaccented syllable in poetry," later (and more correctly) "stressed part of a metrical foot," from Greek thesis "a proposition," also "downbeat" (in music), originally "a setting down, a placing, an arranging; position, situation," from reduplicated form of PIE root *dhe- "to set, put." Sense in logic of "a formulation in advance of a proposition to be proved" is first recorded 1570s; that of "dissertation presented by a candidate for a university degree" is from 1650s.

thespian (n.)

"an actor," 1827, from thespian (adj.). Short form thesp is attested from 1962.

thespian (adj.)

1670s, "of or pertaining to tragedy or dramatic acting," from Greek Thespis, semi-legendary 6c. B.C.E. poet of Icaria in Attica, often called the Father of Greek Tragedy. The literal meaning of the name is "inspired by the gods."

Thessaly

district south of Macedonia and east of Epirus, from Greek Thessalia (Attic Thettalia), an Illyrian name of unknown origin. Related: Thessalian. The city of Thessalonika on the Thermaic Gulf was ancient Therme, renamed when rebuilt by the Macedonian king Cassander, son of Antipater, and named in honor of his wife, Thessalonica, half-sister of Alexander the Great, whose name contains the region name and Greek nikē "victory." The adjectival form of it is Thessalonian Related: Thessalonians.

theta (n.)

eighth letter of the Greek alphabet; in ancient Greece, from Hebrew teth; originally an aspirated -t- (see th). Written on ballots to indicate a vote for a sentence of "death" (thanatos), hence occasional allusive use for "death."

Thetis

name of a sea goddess in Greek mythology, mother of Achilles by Peleus. Since Roman times, sometimes, in poetry, "the sea personified."

theurgy (n.)

1560s, "white magic," from Late Latin theurgia, from Late Greek theourgia "a divine work, a miracle, magic, sorcery," from theos (genitive theou) "a god" (from PIE root *dhes-, forming words for religious concepts) + -ergos "working" (from PIE root *werg- "to do"). From 1858 as "the working of divine forces in human affairs." Related: Theurgical.

thew (n.)

Old English þeaw "usage, custom, habit;" see thews.

thews (n.)

Old English þeawes "customs, habit, manners; morals, conduct, disposition, personal qualities," plural of þeaw "habit, custom," from Proto-Germanic *thawaz (source also of Old Saxon thau "usage, custom, habit," Old High German thau "discipline"). According to OED, with no certain cognates outside West Germanic and of unknown origin. Meaning "bodily powers or parts indicating strength, good physique" is attested from 1560s, from notion of "good qualities." Acquired a sense of "muscular development" when it was revived by Scott (1818).

this (pron.)

Old English þis, neuter demonstrative pronoun and adjective (masc. þes, fem. þeos), probably from a North Sea Germanic pronoun *tha-si-, formed by combining the base *þa- (see that) with -s, which is probably identical with Old English se "the" (representing here "a specific thing"), or with Old English seo, imperative of see (v.) "to behold." Compare Old Saxon these, Old Frisian this, Old Norse þessi, Middle Dutch dese, Dutch deze, Old High German deser, German dieser.

Once fully inflected, with 10 distinct forms; the oblique cases and other genders gradually fell away by 15c. The Old English plural was þæs (nominative and accusative), which in Northern Middle English became thas, and in Midlands and Southern England became thos. The Southern form began to be used late 13c. as the plural of that (replacing Middle English tho, from Old English þa) and acquired an -e (apparently from the influence of Middle English adjective plurals in -e; compare alle from all, summe from sum "some"), emerging early 14c. as modern those.

About 1175 thes (probably a variant of Old English þæs) began to be used as the plural of this, and by 1200 it had taken the form these, the final -e acquired via the same mechanism that gave one to those.

thiamin (n.)

also thiamine, alternative name for vitamin B1, 1937, coined by U.S. chemist Dr. Robert R. Williams (1886-1965) from thio-, indicating the presence of sulfur, from Greek theion "sulfur," + amine, indicating the amino group. Or the second element might be from vitamin.

thick (adj.)

Old English þicce "dense, viscous, solid, stiff; numerous, abundant; deep," also as an adverb, "thickly, closely, often, frequently," from Proto-Germanic *thiku- (source also of Old Saxon thikki, Old High German dicchi, German dick, Old Norse þykkr, Old Frisian thikke), from PIE *tegu- "thick" (source also of Gaelic tiugh). Secondary Old English sense of "close together" is preserved in thickset and proverbial phrase thick as thieves (1833). Meaning "stupid" is first recorded 1590s. Related: Thickly.

As a noun, "the thick part" (of anything), from mid-13c. Phrase through thick and thin, indicating rough or smooth going, hence "unwaveringly," is in Chaucer (late 14c.); thick-skinned is attested from 1540s; in figurative sense from c. 1600. To be in the thick of some action, etc., "to be at the most intense moment" is from 1680s, from a Middle English noun sense.

thickness (n.)

Old English þicness "density, viscosity, hardness; depth; anything thick or heavy; darkness; thicket;" see thick + -ness.

thicken (v.)

late 14c. (transitive), 1590s (intransitive), from thick + -en (1). Related: Thickened; thickening. An earlier verb was Middle English thick, Old English þiccian "to thicken, to crowd together."

thickening (n.)

"substance used to thicken something," 1839, verbal noun from thicken.

thicket (n.)

"close-set growth of shrubs, bushes, trees, etc.," late Old English þiccet, from þicce (see thick) + denominative suffix -et. Absent in Middle English, reappearing early 16c., perhaps a dialectal survival or a re-formation.

thickset (adj.)

also thick-set, late 14c., thikke sette "with parts or things set close together" (of grass on a sward, etc.), from thick + set (v.). Meaning "stocky, strong and square-built" is recorded from 1724.

thief (n.)

Old English þeof "thief, robber," from Proto-Germanic *theuba- (source also of Old Frisian thiaf, Old Saxon thiof, Middle Dutch and Dutch dief, Old High German diob, German dieb, Old Norse þiofr, Gothic þiufs), a word of uncertain origin.

thieve (v.)

Old English þeofian "to thieve, steal," from þeof (see thief). Rare in Old English, rarer in Middle English, not common until 17c.; perhaps the modern word is a late 16c. re-formation. Thieving (adj.) first attested 1520s.

thievery (n.)

1560s, from thieve + -ery. An Old English word for it was þeofend.

thievish (adj.)

mid-15c., "of or pertaining to thieves," from thieve or thief + -ish. Meaning "inclined to steal" is from 1530s. Wycliffe and Chaucer used thiefly (late 14c.). Related: Thievishly; thievishness.

thigh (n.)

Old English þeoh, þeh, from Proto-Germanic *theuham (source also of Old Frisian thiach, Old Dutch thio, Dutch dij, Old Norse þjo, Old High German dioh), probably literally "the thick or fat part of the leg," from PIE *teuk-, from root *teue- "to swell."

thigmotropism (n.)

1900, from thigmo-, combining form meaning "touch," from Greek thigma "touch" + tropism.

thilk (pron., adj.)

"that same, the very thing," early 13c., contraction from þe "the" (see the) + ilce "same" (see ilk).

thimble (n.)

Old English þymel "sheath or covering for the thumb," from thuma (see thumb (n.)) + instrumental suffix -el (1), used in forming names of tools (compare handle (n.)). The unetymological -b- appears mid-15c. (compare humble, nimble, etc.). Originally of leather, metal ones came into use 17c. Related: Thimbleful. Thimblerig, con game played with three thimbles and a pea or button, is attested from 1825 by this name, though references to thimble cheats, probably the same swindle, date back to 1716 (see rig (v.)).

thin (adj.)

Old English þynne "narrow, lean, scanty, not dense; fluid, tenuous; weak, poor," from Proto-Germanic *thunni "thin" (source also of West Frisian ten, Middle Low German dunne, Middle Dutch dunne, Dutch dun, Old High German dunni, German dünn, Old Norse þunnr, Swedish tunn, Danish tynd), from PIE *tnu- "stretched, stretched out" (hence "thin"), from root *ten- "to stretch" (source also of Latin tenuis "thin, slender").

"Loose or sparse," hence "easily seen through," with figurative extensions. Related: Thinly; thinness. Thin-skinned is attested from 1590s; the figurative sense of "touchy" is from 1670s.

thin (v.)

Old English þynnian "to make thin, lessen, dilute," also intransitive, "become thin," from thin (adj.). Intransitive sense of "to become less numerous" is attested from 1743; that of "to become thinner" is recorded from 1804. Compare similarly formed German dünnen, Dutch dunnen. Related: Thinned; thinning.

thine (pron.)

Old English þin, possessive pronoun (originally genitive of þu "thou"), from Proto-Germanic *thinaz (source also of Old Frisian, Old Saxon thin, Middle Dutch dijn, Old High German din, German dein, Old Norse þin), from PIE *t(w)eino-, suffixed form of second person singular pronominal base *tu-. A brief history of the second person pronoun in English can be found here; see also thou.

thing (n.)

Old English þing "meeting, assembly, council, discussion," later "entity, being, matter" (subject of deliberation in an assembly), also "act, deed, event, material object, body, being, creature," from Proto-Germanic *thinga- "assembly" (source also of Old Frisian thing "assembly, council, suit, matter, thing," Middle Dutch dinc "court-day, suit, plea, concern, affair, thing," Dutch ding "thing," Old High German ding "public assembly for judgment and business, lawsuit," German Ding "affair, matter, thing," Old Norse þing "public assembly"). The Germanic word is perhaps literally "appointed time," from a PIE *tenk- (1), from root *ten- "stretch," perhaps on notion of "stretch of time for a meeting or assembly."

The sense "meeting, assembly" did not survive Old English. For sense evolution, compare French chose, Spanish cosa "thing," from Latin causa "judicial process, lawsuit, case;" Latin res "affair, thing," also "case at law, cause." Old sense is preserved in second element of hustings and in Icelandic Althing, the nation's general assembly.

Of persons, often pityingly, from late 13c. Used colloquially since c. 1600 to indicate things the speaker can't name at the moment, often with various meaningless suffixes (see thingamajig).

Things "personal possessions" is from c. 1300. The thing "what's stylish or fashionable" is recorded from 1762. Phrase do your thing "follow your particular predilection," though associated with hippie-speak of 1960s is attested from 1841.

thingamajig (n.)

also thingumajig, 1824, see thing. Compare in similar sense kickumbob (1620s), thingum (1670s), thingumbob (1751), thingummy (1796), jigamaree (1824); such-a-thing (1756).

think (v.)

Old English þencan "imagine, conceive in the mind; consider, meditate, remember; intend, wish, desire" (past tense þohte, past participle geþoht), probably originally "cause to appear to oneself," from Proto-Germanic *thankjan (source also of Old Frisian thinka, Old Saxon thenkian, Old High German denchen, German denken, Old Norse þekkja, Gothic þagkjan).

Old English þencan is the causative form of the distinct Old English verb þyncan "to seem, to appear" (past tense þuhte, past participle geþuht), from Proto-Germanic *thunkjan (source also of German dünken, däuchte). Both are from PIE *tong- "to think, feel" which also is the root of thought and thank.

The two Old English words converged in Middle English and þyncan "to seem" was absorbed, except for its preservation in archaic methinks "it seems to me."

As a noun, think, "act of prolonged thinking," is attested by 1834. The figurative thinking cap is attested from 1839.