Etymology dictionary

information (n.) — initiatory (adj.)

information (n.)

late 14c., informacion, "act of informing, communication of news," from Old French informacion, enformacion "advice, instruction," from Latin informationem (nominative informatio) "outline, concept, idea," noun of action from past participle stem of informare "to train, instruct, educate; shape, give form to" (see inform). The restored Latin spelling is from 16c.

Meaning "knowledge communicated concerning a particular topic" is from mid-15c. The word was used in reference to television broadcast signals from 1937; to punch-card operating systems from 1944; to DNA from 1953. Information theory is from 1950; information technology is from 1958 (coined in "Harvard Business Review"); information revolution, to be brought about by advances in computing, is from 1966. Information overload is by 1967.

informality (n.)

1590s, from informal + -ity.

informer (n.)

late 14c., enfourmer "instructor, one who teaches or gives advice," from inform (Middle English enfourmen) and also from Old French enformeor. Meaning "one who communicates information" is mid-15c.; sense of "one who gives information against another" (especially in reference to law-breaking) is c. 1500.

informed (adj.)

1540s, "current in information," past-participle adjective from inform (v.). In 16c.-17c. it also could mean "unformed, formless," from in- (1) "not, opposite of," and was used in astronomy of stars that did not form part of the visual pattern of a constellation but were within it.

in forma pauperis

legal Latin, literally "in the form of a poor person" (thus exempt from certain court fees, etc.), 1590s; see form (n.) + pauper (n.).

informatics (n.)

1967, translating Russian informatika (1966); see information + -ics.

infortunate (adj.)

"unlucky, luckless," late 14c., from Latin infortunatus, from in- "not, opposite of" (see in- (1)) + fortunatus "prospered, prosperous; lucky, happy" (see fortunate (adj.)). Also used in medieval astrology in reference to the supposed malevolent influence of certain positions or combinations of planets. The word lies beneath the "obsolete" headstone in OED. Related: infortune (n.); infortunacy.

infotainment (n.)

1983, from info- + entertainment.

infra-

word-forming element meaning "below, beneath," from Latin infra (adverb and preposition) "below, underneath, on the under side, beneath," also "later than; smaller than; inferior to," related to infernus "low, below," from PIE *ndher "under" (source also of Sanskrit adnah "below," Old English under "under, among;" see under). Modern popular use of it dates from the 1920s, as an opposite to super-, often in science fiction. "This use of infra- is scarcely a Latin one" [OED].

infra (adv.)

"under, below, further on," from Latin infra "below, under, beneath" (see infra-). A Latin word sometimes encountered in footnotes.

infraction (n.)

mid-15c., "the breaking of an agreement," from Old French infraction (13c.) and directly from Latin infractionem (nominative infractio) "a breaking, weakening," noun of action from past participle stem of infringere "to damage, break off, break, bruise," from in- "in" (from PIE root *en "in") + frangere "to break" (from PIE root *bhreg- "to break"). The verb infract (1560s) is archaic.

infra dig.

"beneath one's dignity, unbecoming to one's position in society," 1824, colloquial abbreviation of Latin infra dignitatem "beneath the dignity of." See infra- + dignity.

infralapsarian (adj.)

1731, from infra- + Latin lapsus "a fall" (see lapse (n.)) + ending from unitarian, etc.

infra-red (adj.)

also infrared, 1873, "below the red" (in the spectrum), from infra- + red (adj.1). As a noun, also from 1873.

infrasonic (adj.)

also infra-sonic, 1920, on the model of supersonic, etc., from infra- + sonic. Or perhaps modeled on French infra-sonore.

infrastructure (n.)

1887, from French infrastructure (1875); see infra- + structure (n.). The installations that form the basis for any operation or system. Originally in a military sense.

infrequency (n.)

1670s, fact of being infrequent," from Latin infrequentia "a small number, thinness, scantiness," abstract noun from infrequentem (nominative infrequens) "occurring seldom, unusual; not crowded, absent," from in- "not" (see in- (1)) + frequens (see frequent). Older in this sense is infrequence (1640s). Earlier infrequency was used in a now-obsolete sense of "state of being unfrequented" (c. 1600).

infrequent (adj.)

1530s, "little used" (now obsolete); 1610s, "not occurring often," from Latin infrequentem (nominative infrequens) "occurring seldom, unusual; not crowded, absent," from in- "not" (see in- (1)) + frequens "repeated, regular, constant, often" (see frequent). Related: Infrequently.

infrigidation (n.)

early 15c., in medicine, "a making cold, cooling; a state of coolness," from Late Latin infrigidationem (nominative infrigidatio) "a cooling," noun of action from past participle stem of infrigidare "to make cold," from in- "in, into" (from PIE root *en "in") + frigidare, from frigidus "cold" (see frigid). A verb infrigidate is attested from 1540s.

infringement (n.)

"a break or breach" (of a contract, right, etc.), from infringe + -ment. Earlier in a now-obsolete sense of "contradiction" (1590s).

infringe (v.)

mid-15c., enfrangen, "to violate," from Latin infringere "to damage, break off, break, bruise," from in- "in" (from PIE root *en "in") + frangere "to break" (from PIE root *bhreg- "to break"). The meaning "encroach" is recorded by c. 1760. Related: Infringed; infringing.

infundibulum (n.)

1799, "funnel-shaped organ or body part," from a Modern Latin use of Latin infundibulum "a funnel," from infundere "to pour into" (see infuse) + -bulum, suffix forming names of instruments. In some cases a loan-translation into Latin of Greek khoane "funnel." Related: Infundibular.

infuriating (adj.)

1874, present-participle adjective from infuriate (v.). Related: Infuriatingly.

infuriation (n.)

1791, noun of action from infuriate (v.).

infuriate (v.)

1660s, from Italian infuriato, from Medieval Latin infuriatus, past participle of infuriare "to madden, enrage," from Latin in furia "in a fury," from ablative of furia (see fury). Also from 1660s as an adjective in English, but this use is rare. Related: Infuriated; infuriating.

infusion (n.)

c. 1400, "a liquid extract (obtained by soaking in water);" early 15c., "a pouring in; that which is poured in," from Old French infusion "injection" (13c.) or directly from Latin infusionem (nominative infusio) "a pouring in, a watering," noun of action from past participle stem of infundere "to pour into" (see infuse).

infuse (v.)

early 15c., "to pour in, introduce, soak (something in liquid)," from Latin infusus, past participle of infundere "to pour into, pour out; press in, crowd in; mix, mingle," from in- "in" (from PIE root *en "in") + fundere "to pour, melt" (from nasalized form of PIE root *gheu- "to pour"). Related: Infused; infusing; infusory; infusorial.

-ing (2)

suffix used to form the present participles of verbs and the adjectives derived from them, from Old English present-participle suffix -ende, from PIE *-nt- (cognates: German -end, Gothic -and, Sanskrit -ant, Greek -on, Latin -ans, -ens). The vowel weakened in late Old English and the spelling with -g began 13c.-14c. among Anglo-Norman scribes who naturally confused it with -ing (1).

-ing (1)

suffix attached to verbs to mean their action, result, product, material, etc., from Old English -ing, also -ung, from Proto-Germanic *-unga-, *-inga- (cognates: Old Norse -ing, Dutch -ing, German -ung). In early use often denoting completed or habitual action; its use has been greatly expanded in Middle and Modern English.

-ing (3)

Old English -ing, patronymic suffix (denoting common origin); surviving in place names (Birmingham, Nottingham) where it denotes "tribe, community."

Inga

fem. proper name, usually a shortening of Ingrid (q.v.).

in-gather (v.)

also ingather, 1570s, from in (adv.) + gather (v.). Related: Ingathered; ingathering (1530s).

ingenious (adj.)

early 15c., "intellectual, talented," from Old French ingenios, engeignos "clever, ingenious" (Modern French ingénieux), from Latin ingeniosus "of good natural capacity, full of intellect, clever, gifted with genius," from ingenium "innate qualities, ability; inborn character," literally "that which is inborn," from in- "in" (from PIE root *en "in") + gignere "to beget" (from PIE *gen(e)-yo-, suffixed form of root *gene- "give birth, beget").

Sense of "skillful, crafty, clever at contrivance" first recorded 1540s; earlier in this sense was Middle English enginous (mid-14c.), from Old French engeignos. Middle English also had engineful "skillful (in war)" (c. 1300). By a direct path, Latin ingenium produced Middle English ingeny "intellectual capacity, cleverness" (early 15c.), but this is obsolete. Compare engine. Related: Ingeniously; ingeniousness.

ingenue (n.)

"young woman who displays innocent candor or simplicity," 1848, from French ingénue "artless girl," especially as a character on the stage, noun use of fem. of ingénu "ingenuous, artless, simple" (13c.), from Latin ingenuus "frank, upright, candid," originally "free-born" (see ingenuous). Italicized in English into 20c.

ingenuity (n.)

1590s, "honor, nobility," from French ingénuité "quality of freedom by birth" and directly from Latin ingenuitatem (nominative ingenuitas) "condition of a free-born man," figuratively "frankness, generosity, noble-mindedness," from ingenuus "frank, candid, noble" (see ingenuous).

Etymologically, this word belongs to ingenuous, but in 17c. ingenious "intellectual, talented" and ingenuous so often were confused (even by Shakespeare) that ingenuity in English has come to mean only "capacity for invention or construction." That sense of this word is first attested 1640s; the word for it in Middle English was ingeniosity (the native word is craftiness). French ingénuité, meanwhile, has evolved through "natural and graceful freedom of manners" to "graceful simplicity" (compare ingenue); for the sense "ingeniousness," French uses ingéniosité.

ingenuous (adj.)

1590s, "noble in nature, high-minded; honorably straightforward," from Latin ingenuus "with the virtues of freeborn people, of noble character, frank, upright, candid," originally "native, freeborn," literally "born in (a place)," from in- "in" (from PIE root *en "in") + PIE *gen(e)-wo-, suffixed form of root gene- "to give birth, beget, produce" (see genus). Sense of "artless, innocent" is 1670s, via evolution from "honorably open, straightforward," to "innocently frank." Related: Ingenuously; ingenuousness.

ingest (v.)

1610s, "to take in as food," from Latin ingestus, past participle of ingerere "to throw in, pour in, heap upon," from in- "into" (from PIE root *en "in") + gerere "to carry" (see gest). Related: Ingested; ingesting.

ingestion (n.)

"action of ingesting," 1610s, from Late Latin ingestionem (nominative ingestio) "a pouring in," noun of action from past participle stem of ingerere "pour in" (see ingest).

ingle (n.1)

"fireplace," c. 1500, from Scottish, usually said to be from Gaelic aingeal "fire, light" ("but there are difficulties" [OED]), a word of uncertain origin. The vogue for Scottish poetry in late 18c. introduced ingleside "fireside" (1747) and ingle-nook, inglenook "corner by the fire" (1773) to literary English.

ingle (n.2)

"boy favorite, catamite," 1590s, of uncertain origin.

inglorious (adj.)

"with bad fame, dishonorable," 1570s, from in- (1) "not, opposite of" + glorious. Latin ingloriosus meant "without fame, unhonored, inconspicuous, without trophies." The classical sense "without fame, obscure" is attested in the English word from 1590s but is marked "rare" in OED. Related: Ingloriously; ingloriousness.

in-going (adj.)

also ingoing, 1825, from in + going. Probably a modern formation unrelated to Middle English in-going (n.) "act of entering" (mid-14c.), from ingo "to go in, enter," from Old English ingan (past tense ineode), equivalent of German eingehen, Dutch ingaan.

ingot (n.)

late 14c., "mold in which metal is cast," probably from in- (2) "in" + Old English goten, past participle of geotan "to pour" (from PIE root *gheu- "to pour"). Sense of "mass of cast metal" first attested early 15c.

ingraft (v.)

see engraft. Related: ingrafted; ingrafting.

ingrain (v.)

see engrain, or ingrained.

ingrained (adj.)

"deeply rooted," 1590s, literally "dyed with grain "cochineal," the red dyestuff (see engrain). Figuratively, "thoroughly imbued" (of habits, principles, prejudices, etc.) from 1851. In reference to dyed carpets, etc., it is attested from 1766, from the manufacturing phrase in (the) grain "in the raw material before manufacture."

ingrate (n.)

"ungrateful person," 1670s, from earlier adjective meaning "unfriendly," also "ungrateful, unthankful" (14c.), from Latin ingratus "unpleasant, disagreeable," also "ungrateful, unthankful," and "thankless, unprofitable," from in- "not" (see in- (1)) + gratus "pleasing, beloved, dear, agreeable" (from suffixed form of PIE root *gwere- (2) "to favor").

ingratiation (n.)

1804, noun of action from ingratiate (v.).

ingratiate (v.)

1620s, possibly via 16c. Italian ingraziarsi "to bring (oneself) into favor," or an unrecorded Medieval Latin *ingratiatus, from Latin phrase in gratiam "for the favor of," from in "in" (from PIE root *en "in") + gratia "favor, grace" (from suffixed form of PIE root *gwere- (2) "to favor"). Related: Ingratiated; ingratiating.

ingratitude (n.)

mid-14c., from Old French ingratitude "ungratefulness" (13c.) and directly from Late Latin ingratitudinem (nominative ingratitudo) "unthankfulness," noun of quality from Latin ingratus "ungrateful" (see ingrate).

ingrave (v.)

see engrave. Related: Ingraved; ingraving.

ingredient (n.)

in early use also engredient, early 15c., "something forming part of a mixture," from Latin ingredientem (nominative ingrediens) "that which enters into" (a compound, recipe, etc.), present participle of ingredi "go in, enter," from in- "in" (from PIE root *en "in") + gradi "to step, go" (from PIE root *ghredh- "to walk, go"). Also from early 15c. as an adjective, "forming part of a mixture."

ingress (n.)

mid-15c., from Latin ingressus "an advance; walking; an entry," from ingress-, past participle stem of ingredi "to step into, enter," from in- "in" (from PIE root *en "in") + gradi "to step, go" (from PIE root *ghredh- "to walk, go"). The verb meaning "to enter, go in" sometimes said to be American English, but it is attested from early 14c.

Ingrid

fem. proper name, Scandinavian or German, from Ing, Germanic god-name (Old Norse Yngvi, Old English Ingwine), apparently an earlier name of Freyr. He was associated with prosperity, virility, and fertility. Second element in the name is either friðr "fair, beautiful" or rida "to ride." As a given name for girls in the U.S., almost unknown before 1940 (about the time Swedish actress Ingrid Bergman rose to fame in Hollywood); it was most popular in 1960s and early '70s but never common.

ingrown (adj.)

also in-grown, 1660s, "native, innate," from in + grown. Of nails, "that has grown into the flesh," 1869 (in-growing in this sense is from 1847). Related: Ingrowth (1870).

inguinal (adj.)

1680s, from French inguinal (16c.) or directly from Latin inguinalis "of the groin," from inguen (genitive inguinis) "groin," from PIE *engw- "groin; internal organ" (which is perhaps also the source of Greek adēn "gland"). Related: Inguinally.

ingurgitation (n.)

"immoderate eating and drinking," 1520s, from Late Latin ingurgitationem (nominative ingurgitatio), noun of action from past participle stem of Latin ingurgitare "plunge into, gorge," from in- "in, into" (from PIE root *en "in") + gurgitare "to engulf," from gurges "whirlpool, gorge" (see gurges).

Ingvaeonic (n.)

hypothetical ancestral North Sea Germanic language, 1933, from Latin Ingaeuones, name of a Germanic tribe in Tacitus, literally "people of Yngve," god, demigod, or eponymous ancestor. Earlier the word was used in English in reference to North Sea Germanic tribes (1904).

inhabitant (n.)

"one who dwells in a place" (as distinguished from a visitor or transient), early 15c., from Anglo-French inhabitant, from Latin inhabitantem (nominative inhabitans), present participle of inhabitare "to dwell in" (see inhabit). Related: Inhabitants. As an adjective, also from early 15c.

inhabitable (adj.)

1. "not habitable," late 14c., from Old French inhabitable (14c.), from Latin inhabitabilis, from in- "not, opposite of" (see in- (1)) + habitabilis (see habitable).

2. "capable of being inhabited" (the main modern sense), c. 1600, from inhabit + -able). In Late Latin, inhabitabilis also was used in a sense of "that can be inhabited." A word used in two opposite senses.

inhabit (v.)

late 14c., from Old French enhabiter, enabiter "dwell in, live in, reside" (12c.), from Latin inhabitare "to dwell in," from in- "in" (from PIE root *en "in") + habitare "to dwell," frequentative of habere "to hold, have" (from PIE root *ghabh- "to give or receive"). Formerly also enhabit. Related: Inhabited; inhabiting.

inhalation (n.)

1620s, "a breathing in," noun of action from past participle stem of Latin inhalare "breathe upon" (used here as if it meant "to breathe in"), from in- "on, upon" (from PIE root *en "in") + halare "breathe."

inhale (v.)

1725, "to breathe in, draw air into the lungs," a back-formation from inhalation or else from French inhaler in this sense; used as a word to be the opposite of exhale. Slang sense of "eat rapidly" is recorded from 1924. As a noun, "act of inhaling," by 1904. Related: Inhaled; inhaling.

inhalant (adj.)

1804, from Latin inhalantem, present participle of inhalare (see inhale). As a noun from 1830.

inhance (v.)

obsolete form of enhance. Related: Inhancement.

inharmonious (adj.)

1711, from in- (1) "not" + harmonious. Related: Inharmoniously.

inherence (n.)

1570s, from French inhérence (15c.) or directly from Medieval Latin inhaerentia, from inhaerentem (see inherent). Related: Inherency (c. 1600).

inherent (adj.)

1570s, from Latin inhaerentem (nominative inhaerens), present participle of inhaerere "be closely connected with, be inherent," literally "adhere to, cling to," from in- "in" (from PIE root *en "in") + haerere "to adhere, stick" (see hesitation). Related: Inherently.

inhere (v.)

1580s, "to exist or have being" (in something), "belong to the intrinsic nature of," from Latin inhaerere "to stick in or to," also figurative (see inherent). Related: Inhered; inhering.

inherit (v.)

c. 1300, "to make (someone) an heir" (a sense now obsolete), from Old French enheriter "make heir, attribute the right of inheretance to, appoint as heir," from Late Latin inhereditare "to appoint as heir," from in- "in" (from PIE root *en "in") + Latin hereditare "to inherit," from heres (genitive heredis) "heir" (see heredity).

Sense of "receive inheritance, get by succession as representative of the former possessor" is attested from mid-14c.; in Medieval Latin inhereditare also had taken on a sense "put in possession." Original sense is retained in disinherit. Related: Inherited; inheriting; inheritable.

inheritance (n.)

late 14c., enheritaunce "fact of receiving by hereditary succession;" early 15c. as "that which is or may be inherited," from Anglo-French and Old French enheritaunce, from Old French enheriter "make heir, appoint as heir" (see inherit). Heritance "act of inheriting" is from mid-15c.

inhesion (n.)

1630s, from Late Latin inhaesionem (nominative inhaesio) "a hanging or adhering to," noun of action from past participle stem of Latin inhaerere "to stick in or into" (see inherent).

inhibition (n.)

late 14c., "formal prohibition; interdiction of legal proceedings by authority;" also, the document setting forth such a prohibition, from Old French inibicion and directly from Latin inhibitionem (nominative inhibitio) "a restraining," from past participle stem of inhibere "to hold in, hold back, keep back," from in- "in, on" (from PIE root *en "in") + habere "to hold" (from PIE root *ghabh- "to give or receive"). Psychological sense of "involuntary check on an expression of an impulse" is from 1876.

inhibit (v.)

early 15c., "to forbid, prohibit," back-formation from inhibition or else from Latin inhibitus, past participle of inhibere "to hold in, hold back, keep back," from in- "in, on" (from PIE root *en "in") + habere "to hold" (from PIE root *ghabh- "to give or receive"). Psychological sense (1876) is from earlier, softened meaning of "restrain, check, hinder" (1530s). Related: Inhibited; inhibiting.

inhibitor (n.)

1868 as a Scottish legal term; 1914 in biochemistry; agent noun in Latin form from inhibit. Form inhibiter is attested from 1610s.

inhibitory (adj.)

late 15c., from Medieval Latin inhibitorius "inhibitory," from inhibit-, past participle stem of Latin inhibere "to hold in, keep back" (see inhibition).

inhospitable (adj.)

1560s, from French inhospitable (15c.), from Medieval Latin inhospitabilis (equivalent of Latin inhospitalis), from in- "not" (see in- (1)) + Medieval Latin hospitabilis (see hospitable).

in-house (adj.)

also inhouse, 1955, from in (prep.) + house (n.).

inhumation (n.)

"act of burying in the ground" (as opposed to cremation), 1630s, noun of action from inhume "to bury," literally "to put into the ground," from in- "in" (from PIE root *en "in") + humus "earth, soil" (see humus).

inhume (v.)

"bury, lay in the grave," c. 1600, from Latin inhumare "to bury," literally "to put into the ground," from in- "in" (from PIE root *en "in") + humus "earth, soil" (see humus). Related: Inhumed; inhuming.

inhumanity (n.)

"barbarous cruelty," late 15c., from French inhumanité (14c.) or directly from Latin inhumanitatem (nominative inhumanitas) "inhuman conduct, savageness; incivility, rudeness," noun of quality from inhumanus "inhuman, savage, cruel" (see inhuman).

inhumane (adj.)

originally a variant spelling and pronunciation of inhuman "cruel, hard-hearted;" it appears to have died out 17c. but returned c. 1822, probably a reformation as a negative of humane (q.v.), with its accent.

inhuman (adj.)

mid-15c., "cruel," from Latin inhumanus "inhuman, savage, cruel, rude, barbarous, uncultured," from in- "not, opposite of" (see in- (1)) + humanus "human" (see human (adj.)). Spelled inhumane till 18c. (see humane).

Inigo

masc. proper name, from Spanish Iñigo, probably from Latin Ignatius.

inimical (adj.)

1640s, from Late Latin inimicalis "hostile," from Latin inimicus "unfriendly; an enemy" (see enemy).

inimitability (n.)

1711, from inimitable + -ity. Perhaps from or modeled on French inimitabilité.

inimitable (adj.)

late 15c., from Latin inimitabilis "that cannot be imitated," from in- "not, opposite of" (see in- (1)) + imitabilis "imitable" (see imitable). Related: Inimitably.

iniquity (n.)

c. 1300, "hostility, malevolence; a hostile action," from Old French iniquité, iniquiteit "wickedness; unfavorable situation" (12c.), from Latin iniquitatem (nominative iniquitas) "unequalness, unevenness," figuratively "unfavorableness, unfairness, injustice," noun of quality from iniquus "unjust, unequal; slanting, steep," from in- "not" (see in- (1)) + aequus "just, equal" (see equal (adj.)).

For the vowel change in the Latin compound, see acquisition. Meaning "evil, wickedness" is from late 14c. Old Iniquity (1610s) was a comic or buffoonish character in old morality plays, representing vice.

iniquitous (adj.)

"unjust, wicked," 1670s, from iniquity + -ous. Earlier were iniquous (1650s, from Latin iniquus) and inique (1520s, from French inique). Related: Iniquitously; iniquitousness.

initiate (n.)

"one who has been initiated" (in secret doctrines, etc.), 1732, from obsolete or archaic past-participle adjective initiate "initiated, instructed in secret knowledge" (c. 1600), from Latin initiatus (see initiate (v.)).

initialize (v.)

"to make ready for operation," 1957, from initial (adj.) + -ize. The same formation had been used earlier to mean "use initials instead of a name" (1837); "designate by initials" (1833). Related: Initialized; initializing; initialization (1957 in the modern sense).

initial (v.)

"to mark or sign with initials," 1837, from initial (n.). Related: Initialed; initialing.

initial (n.)

"initial letter of a name or surname," 1620s, from initial (adj.) in a specialized sense "standing at the beginning of a word, sentence, etc." (1620s).

initial (adj.)

1520s, "of or pertaining to a beginning," from French initial or directly from Latin initialis "initial, incipient, of the beginning," from initium "a beginning, a commencement; an entrance, a going in," noun use of neuter past participle of inire "to go into, enter upon, begin," from in- "into, in" (from PIE root *en "in") + ire "to go" (from PIE root *ei- "to go"). Related: Initially.

initiative (n.)

"power of initiating," 1775, from French initiative (16c.), from Latin initiatus, past participle of initiare "to begin," from initium "a beginning" (see initial (adj.)). From 1793 as "disposition to take the lead." Phrase take the initiative recorded by 1815.

initiation (n.)

1580s, from French initiation or directly from Latin initiationem (nominative initiatio) "participation in secret rites," noun of action from past-participle stem of initiare "originate, initiate," from initium "a beginning" (see initial (adj.)).

initiate (v.)

c. 1600, "introduce to some practice or system," also "begin, set going," from Late Latin initiatus, past participle of initiare "to begin, originate," in classical Latin only in the sense "to instruct in mysteries or sacred knowledge." This is from initium "a beginning; an entrance," also in plural initia "constituent parts; sacred mysteries," a noun use of the neuter past participle of inire "to go into, enter upon, begin," from in- "into, in" (from PIE root *en "in") + ire "to go" (from PIE root *ei- "to go").

In some senses the English word is a back-formation from initiation. Related: Initiated; initiates; initiating; initiator.

initialism (n.)

"written word formed from the first letters, in order, of other words in a name or phrase," 1957, from initial (n.) + -ism. The word was used earlier in a sense "group of initial letters of an author's name (rather than the full name) on a publication" (1868). An earlier term for what we now call an initialism was alphabetic abbreviation (1907).

The distinction from acronym is not universally agreed-upon; but in general, cases such as NATO, where the letters always are sounded as a word, are regarded as acronyms, those such as FBI, where the letters sound as letters, are initial-words or initialisms. The use of acronym in entries in this dictionary that are technically initialisms is a deliberate error, because many people will search all such words using "acronym."