Online Etymology Dictionary

inquest (n.): late 13c., enquest, an-queste "legal or judicial inquiry," especially one before a jury, from Old French enqueste "inquiry" (Modern French enquête), from Vulgar Latin *inquaestia (source also of Italian inchiesta), from Latin inquisita (res) "(a thing) looked into; an inquiry," from fem. past participle of Latin inquirere "to seek after, search for" (see inquire). The form with in- prevailed from 18c.
inquire (v.): c. 1300, enqueren, anqueren, "to ask (a question), ask about, ask for (specific information); learn or find out by asking, seek information or knowledge; to conduct a legal or official investigation (into an alleged offense)," from Old French enquerre "ask, inquire about" (Modern French enquérir) and directly from Medieval Latin inquerere, from in- "into" (see in- (2)) + Latin quaerere "ask, seek" (see query (v.)), in place of classical Latin inquirere "seek after, search for, examine, scrutinize." The English word was respelled 14c. on the Latin model, but half-Latinized enquire persists. Related: Inquired; inquiring.
inquisition (n.): late 14c., "judicial investigation, act or process of inquiring," from Old French inquisicion "inquiry, investigation" (12c., Modern French inquisition), from Latin inquisitionem (nominative inquisitio) "a searching into, a seeking; legal examination, a seeking of grounds for accusation," noun of action from past participle stem of inquirere (see inquire).

In Church history, inquisitors were appointed from 382 C.E. to root out heretics; the ecclesiastical court appointed 13c. by Innocent III to suppress heresy never operated in Britain. The English word began to be used in this sense (and with a capital initial letter) after c. 1500, and usually refers to the office's reorganization 1478-1483 in Spain, where it fell under the control of the state as what is commonly called the Spanish Inquisition, noted especially for its severity, secrecy, and the number of its victims.
inquisitive (adj.): late 14c., from Old French inquisitif, from Late Latin inquisitivus "making inquiry," from Latin inquisit-, past participle stem of inquirere "seek after, search for; examine, investigate" (see inquire).
An housbonde shal nat been Inquisityf of goddes pryuetee nor of his wyf. [Chaucer, "Miller's Prologue"]
Related: Inquisitively; inquisitiveness.
inroad (n.): 1540s, "hostile incursion, raid, foray," from in- (2) "in;" second element is road (n.) in the obsolete sense of "riding;" related to raid (v.). Related: Inroads.
insane (adj.): 1550s, of persons, "mentally damaged," from Latin insanus "mad, insane, of unsound mind; outrageous, excessive, extravagant," from in- "not" (see in- (1)) + sanus "well, healthy, sane" (see sane). In reference to actions, "irrational, evidencing madness," from 1842 in English. The noun meaning "insane person" is attested from 1786. For the notion of insanity as sickness, compare lunatic; and Italian pazzo "insane," originally a euphemism, from Latin patiens "suffering." German verrückt, literally past participle of verrücken "to displace," "applied to the brain as to a clock that is 'out of order' " [Buck].
insatiable (adj.): early 15c., insaciable, from Old French insaciable "ravenous" (15c., Modern French insatiable), or directly from Latin insatiabilis "not to be satisfied," from in- "not, opposite of" (see in- (1)) + satiabilis, from satiare (see satiate). Related: Insatiably; insatiableness.
inscription (n.): late 14c., from Latin inscriptionem (nominative inscriptio) "a writing upon, inscription," noun of action from past participle stem of inscribere "inscribe, to write on or in (something)," from in- "in" (see in- (2)) + scribere "to write" (see script (n.)). Related: Inscriptional.
inscrutable (adj.): "that cannot be discovered by searching, mysterious," c. 1500, from Late Latin inscrutabilis, from in- "not, opposite of" (see in- (1)) + *scrutabilis, from scrutari "examine, ransack" (see scrutiny). Related: Inscrutably; inscrutableness.
insect (n.): c. 1600, from Latin (animal) insectum "(animal) with a notched or divided body," literally "cut into," noun use of neuter past participle of insectare "to cut into, to cut up," from in- "into" (see in- (2)) + secare "to cut" (see section (n.)).

The Latin word is Pliny's loan-translation of Greek entomon "insect" (see entomology), which was Aristotle's term for this class of life, in reference to their "notched" bodies. First in English in 1601 in Holland's translation of Pliny. In zoology, in reference to a class of animals, 1753. Translations of Aristotle's term also form the usual word for "insect" in Welsh (trychfil, from trychu "cut" + mil "animal"), Serbo-Croatian (zareznik, from rezati "cut"), Russian (nasekomoe, from sekat "cut"), etc. Insectarian "one who eats insects" is attested from 1893.

Among the adjectival forms that have been tried in English (and mostly rejected by disuse) are insectile (1620s), insectic (1767), insective (1834), insectual (1849), insectine (1853), insecty (1859), insectan (1888).
insecure (adj.): 1640s, "unsafe," also "not fully assured, not free from fear or doubt," from Medieval Latin insecurus, from in- "not" (see in- (1)) + Latin securus (see secure (adj.)). Psychological sense dates from 1935. (insecurity in the psychological sense dates from 1917.) Related: Insecurely.
insensate (adj.): 1510s, "lacking or deprived of physical senses," from Late Latin insensatus "irrational, foolish," from in- "not" (see in- (1)) + sensatus "gifted with sense" (see sensate).

Meaning "irrational, maniacle, lacking or deprived of mental sense" is from 1520s; meaning "lacking or deprived of moral sense, unfeeling" is from 1550s. Insensate means "not capable of feeling sensation," often "inanimate;" insensible means "lacking the power to feel with the senses," hence, often, "unconscious;" insensitive means "having little or no reaction to what is perceived by one's senses," often "tactless." Related: Insensately; insensateness.
insensible (adj.): c. 1400, "lacking the power to feel with the senses, numb, dazed" (now rare in this meaning), from Late Latin insensibilis "that cannot be felt," from in- "not" (see in- (1)) + sensibilis "having feeling: perceptible by the senses" (see sensible). Meaning "void of feeling, not susceptible to emotion or passion" is from 1610s. Meaning "incapable of being felt or perceived by the senses or the mind, so small or slight as to be imperceptible" is from late 14c. Compare insensate.
insensitive (adj.): c. 1600, "having little or no reaction to what is perceived by one's senses," from in- (1) "not, opposite of" + sensitive. For sense, see insensate. From 1834 as "having little or no mental or moral sensitiveness;" meaning "without consideration for the feelings of others" attested by 1974. Related: Insensitively.
inseparable (adj.): mid-14c., from Latin inseparabilis "that cannot be separated," from in- "not, opposite of" (see in- (1)) + separabilis, from separare "to pull apart" (see separate (v.)). Related: Inseparably.
insert (v.): "to set in, put or place in," 1520s, from Latin insertus, past participle of inserere "to graft, implant," from in- "in" (see in- (2)) + serere "attach, join; arrange, line up," from PIE *ser- (3) "to line up" (see series). Middle English had inseren "to set in place, to graft, to introduce (into the mind)" (late 14c.), directly from the Latin verb. Related: Inserted; inserting.
inset (n.): 1550s, "influx of water; place where water flows in," from in (prep.) + set (n.2). The later word in a sense "that which is set in" ("extra pages of a book, etc.," 1871; "small map in the border of a larger one," 1872) probably are a separate formation. In Old English insetan (Old Northumbrian insetta) meant "an institution," literally "a setting in," and perhaps a loan-translation of the source of institution. Similar formation in German einsetzen "to use, employ; institute, begin; install."
inshallah (interj.): 1818, phonetic spelling of Arabic in sha Allah "if Allah wills (it)."
inside (n.): late 14c., ynneside "interior part (of the body)," compound of in (prep.) + side (n.). General sense "inner side or part (of anything)" is from c. 1500.

The adjective sense "being on the inside" is from 1610s, from the noun. It began to be used in slang c. 1900 in reference to the supposed real facts or situation that only an insider would know. Inside man is from 1911 (originally in reference to workers used by management to sniff out union activity); inside job "robbery, espionage, etc., committed by or with the help of a resident or servant of a place" is attested by 1887, American English (also, late 19c., early 20c., "indoors work"). The figurative inside track "advantage" (1854) however is a metaphor from horse racing (1830); inside lanes are shorter than the outer ones on a curved track. Adverbial use in American English inside of (in reference to time) is from 1839.
insidious (adj.): 1540s, from Middle French insidieux "insidious" (15c.) or directly from Latin insidiosus "deceitful, cunning, artful, treacherous," from insidiae (plural) "plot, snare, ambush," from insidere "sit on, occupy," from in- "in" (see in- (2)) + sedere "to sit" (see sedentary). Figurative, usually with a suggestion of lying in wait and the intent to entrap. Related: Insidiously; insidiousness.
insight (n.): c. 1200, innsihht, "sight with the 'eyes' of the mind, mental vision, understanding from within," from in (prep.) + sight (n.). But the meaning often seems to be felt as "sight into" (something else), and so the sense shifted to "penetrating understanding into character or hidden nature" (1580s). Similar formation in Dutch inzigt, German einsicht, Danish indsigt.
insignia (n.): 1640s, from Latin insignia, neuter plural of insigne "badge of honor or office, mark, proof, sign, token," from in- "in" (see in- (2)) + signum "mark" (see sign (n.)). The classically correct singular is insigne.
insignificant (adj.): 1650s, "without meaning," also "answering to no purpose," from in- (1) "not, opposite of" + significant. From 1748 as "small in size." Related: Insignificantly.
insincere (adj.): 1620s (implied in insincerely), from Latin insincerus "spoiled, corrupted; not genuine, not pure, adulterated," from in- "not" (see in- (1)) + sincerus "genuine, candid" (see sincere). Related: Insincerely.
insinuate (v.): 1520s, "to covertly and subtly introduce into the mind or heart" (trans.), from Latin insinuatus, past participle of insinuare "to thrust in, push in, make a way; creep in, intrude, bring in by windings and curvings, wind one's way into," from in- "in" (see in- (2)) + sinuare "to wind, bend, curve," from sinus "a curve, winding" (see sinus).

Intransitive meaning "hint obliquely" is from 1560s. Meaning "maneuver (someone or something) into some desired position or condition" is from 1570s. Physical or literal sense of "to introduce tortuously or indirectly" is from 1640s. Related: Insinuated; insinuating.
insipid (adj.): 1610s, "without taste or perceptible flavor," from Middle French insipide "insipid" (16c.), from Late Latin inspidus "tasteless," from in- "not" (see in- (1)) + Latin sapidus "tasty," from sapere "have a taste" (also "be wise;" see sapient). Figurative meaning "uninteresting, dull" first recorded in English 1640s, probably from Medieval Latin or the Romance languages, where it was a secondary sense.
In ye coach ... went Mrs. Barlow, the King's mistress and mother to ye Duke of Monmouth, a browne, beautifull, bold, but insipid creature. [John Evelyn, diary, Aug. 18, 1649]
Related: Insipidly.
insist (v.): 1580s, from French insister (14c.) or directly from Latin insistere "take a stand, stand on, stand still; follow, pursue; insist, press vigorously, urge, dwell upon," from in- "upon" (see in- (2)) + sistere "take a stand" (see assist (v.)). Perhaps in some cases a back-formation from insistence. Related: Insisted; insisting.
insolent (adj.): late 14c., "contemptuous, arrogant, showing haughty disregard of others," from Latin insolentem (nominative insolens) "arrogant, immoderate," also "unaccustomed, unwonted," literally "unusual, unfamiliar," from in- "not, opposite of" (see in- (1)) + solentem, present participle of solere "be accustomed, be used to; cohabit with," from Proto-Italic *sol-e-.

This is of uncertain origin. An old guess connects it to the source of Latin sodalis "close companion," and suescere "become used to," but de Vaan rejects this on phonetic grounds. Another guess connects it to the source of Latin solum "ground," with a possible sense shift from "inhabit" to "be accustomed to." Or it might be from PIE root *sel- (1) "human settlement" (source also of Old Church Slavonic selo "courtyard, village," Russian selo "village," Old English sele, Old High German sal "hall, house"). Meaning "contemptuous of rightful authority" is from 1670s. Related: Insolently.
Insolent is now chiefly used of language that is intentionally and grossly rude, defiant, or rebellious. Where it applies to conduct, the conduct includes language as the most offensive thing. [Century Dictionary, 1902]
insoluble (adj.): late 14c., "indestructible, unable to be loosened," also figuratively, of problems, etc., "incapable of being solved or explained," from Old French insoluble or directly from Latin insolubilis "that cannot be loosened," from in- "not" (see in- (1)) + solubilis "that can be loosened" (see soluble).
It was a tacit conviction of the learned during the Middle Ages that no such thing as an insoluble question existed. There might be matters that presented serious difficulties, but if you could lay them before the right man -- some Arab in Spain, for instance, omniscient by reason of studies into the details of which it was better not to inquire -- he would give you a conclusive answer. The real trouble was only to find your man. [Gertrude Bell, "The Desert and the Sown," 1907]
Meaning "incapable of being dissolved in a liquid" is from 1713.
insolvent (adj.): 1590s, "unable to pay one's debts," from in- (1) "not" + Latin solventem "paying" (see solvent). Originally of one who was not a trader; only traders could become bankrupt.
insomnia (n.): "chronic inability to sleep," 1620s, insomnie, from Latin insomnia "want of sleep, sleeplessness," from insomnis "sleepless," from in- "not" (see in- (1)) + somnus "sleep" (see Somnus). The re-Latinized form is from 1758.
insouciance (n.): 1820, from French insouciance "heedless indifference or unconcern," from insouciant "carelessness, thoughtlessness, heedlessness," from in- "not" (see in- (1)) + souciant "caring," present participle of soucier "to care," from Latin sollicitare "to agitate" (see solicit).
inspection (n.): late 14c., from Old French inspeccion "inspection, examination" (13c., Modern French inspection), from Latin inspectionem (nominative inspectio) "a looking into," noun of action from past participle stem of inspicere "look at, observe, view; look into, inspect, examine," from in- "into" (see in- (2)) + specere "to look" (see scope (n.1)). Related: Inspectional.
inspiration (n.): c. 1300, "immediate influence of God or a god," especially that under which the holy books were written, from Old French inspiracion "inhaling, breathing in; inspiration" (13c.), from Late Latin inspirationem (nominative inspiratio), noun of action from past participle stem of Latin inspirare "blow into, breathe upon," figuratively "inspire, excite, inflame," from in- "in" (see in- (2)) + spirare "to breathe" (see spirit (n.)).
And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. [Gen. ii.7]
The sense evolution seems to be from "breathe into" to "infuse animation or influence," thus "affect, rouse, guide or control," especially by divine influence. Inspire (v.) in Middle English also was used to mean "breath or put life or spirit into the human body; impart reason to a human soul." Literal sense "act of inhaling" attested in English from 1560s. Meaning "one who inspires others" is attested by 1867.
instability (n.): early 15c., from Old French instabilité "inconstancy" (15c.) or directly from Latin instabilitatem (nominative instabilitas) "unsteadiness," from instabilis "unsteady, not firm, inconstant, fickle," from in- "not, opposite of" (see in- (1)) + stabilis (see stable (adj.)).
install (v.): also instal, formerly also enstall, early 15c., "place in (ecclesiastical) office by seating in an official stall," from Old French installer (14c.) or directly from Medieval Latin installare, from Latin in- "in" (see in- (2)) + Medieval Latin stallum "stall," from a Germanic source (compare Old High German stal "standing place;" see stall (n.1)). Related: Installed; installing.
In the church of England the installation of a canon or prebendary of a cathedral consists in solemnly inducting him into his stall in the choir and his place in the chapter. [Century Dictionary]
installment (n.): also instalment, 1580s, "induction into office, act of installing," from install + -ment.

The word meaning "a partial payment on account of debt due" (1776) earlier referred to the arrangement of payment (1732), and is an alteration of Anglo-French estaler "to fix payments," from Old French estal "fixed position, place; stall of a stable, market, or choir," from a Germanic source akin to Old High German stal "standing place" (see stall (n.1)). General sense of "a part of a whole, furnished or produced in advance of the rest" is from 1823. Installment plan is from 1894.
Instamatic: 1962, proprietary name (reg. Eastman Kodak Co., Rochester, N.Y.) for a type of self-loading camera, from instant + automatic.
instance (n.): late 14c., "urgency, insistence" (a sense now archaic), from Old French instance "effort, application; urgency, eagerness, anxiety" (13c.), from Latin instantia "presence, effort, intention; earnestness, urgency," literally "a standing near," from instans (see instant).

In logic, "a fact, a case, an example" (a sense in English from early 15c.), from Medieval Latin instantia, which translated Greek enstasis. This led to for instance "as an example" (1650s), and the noun phrase give (someone) a for instance (1953, American English). The general sense "anything that illustrates a general type" was in use by 19c.
instant (n.): late 14c., "moment in time, infinitely short space of time," from noun use of Old French instant "near, immediate, at hand; assiduous, urgent" (see instant (adj.)). Related: Instanted; instanting.
instead (adv.): 1590s, contraction of Middle English prepositional phrase ine stede (early 13c.; see stead), itself a loan-translation of Latin in loco (French en lieu de). Typically written as two words until mid-17c.
instep (n.): "arch of the foot," mid-15c., apparently from in + step, "though this hardly makes sense" [Weekley]. An Old English word for "instep" was fotwelm. Middle English also had a verb instep "to track, trace" (c. 1400). Old English instæpe (n.) meant "an entrance."
instigation (n.): early 15c., "urging, incitement; impelling force," from Middle French instigation "instigation," and directly from Latin instigationem (nominative instigatio), noun of action from past participle stem of instigare "urge on, incite," from in- "in" (see in- (2)) + *stigare, a root meaning "to prick," from PIE root *steig- "to prick, stick, pierce" (see stick (v.)).
instill (v.): also instil, early 15c., "to introduce (liquid, feelings, etc.) little by little," from Latin instillare "put in by drops; to drop, trickle," from in- "in" (see in- (2)) + stilla "a drop" (see distill). Related: Instilled; instiller; instilling.
instinct (n.): early 15c., "a prompting" (a sense now obsolete), from Old French instinct (14c.) or directly from Latin instinctus "instigation, impulse, inspiration," noun use of past participle of instinguere "to incite, impel," from in- "into, in, on, upon" (see in- (2)) + stinguere "prick, goad," from PIE *steig- "to prick, stick, pierce" (see stick (v.)).

Meaning "animal faculty of intuitive perception" is from mid-15c., from notion of "natural prompting." General sense of "natural tendency" is first recorded 1560s.
Instinct is said to be blind--that is, either the end is not consciously recognized by the animal, or the connection of the means with the end is not understood. Instinct is also, in general, somewhat deficient in instant adaptability to extraordinary circumstances. [Century Dictionary]
institute (v.): early 14c., "to establish in office, appoint," from Latin institutus, past participle of instituere "to set up, put in place; arrange; found, establish; appoint, designate; govern, administer; teach, instruct," from in- "in" (see in- (2)) + statuere "establish, to cause to stand," from PIE root *stā- "to stand," with derivatives meaning "place or thing that is standing" (see stet). General sense of "set up, found, introduce" first attested late 15c. Related: Instituted; instituting.
institution (n.): c. 1400, "action of establishing or founding (a system of government, a religious order, etc.)," from Old French institucion "foundation; thing established" (12c.), from Latin institutionem (nominative institutio) "a disposition, arrangement; instruction, education," noun of state from institutus (see institute (v.)).

Meaning "established law or practice" is from 1550s. Meaning "establishment or organization for the promotion of some charity" is from 1707. Jocular or colloquial use for "anything that's been around a long time" is from 1837.
instruction (n.): c. 1400, instruccioun, "action or process of teaching," from Old French instruccion (14c., Modern French instruction), from Latin instructionem (nominative instructio) "an array, arrangement," in Late Latin "teaching," from past participle stem of instruere "arrange, prepare, set in order; inform, teach," from in- "on" (see in- (2)) + struere "to pile, build" (see structure (n.)).
Teaching is the general word for the imparting of knowledge .... Instruction has the imparting of knowledge for its object, but emphasizes, more than teaching, the employment of orderly arrangement in the things taught. [Century Dictionary]
Meaning "an authoritative direction telling someone what to do; a document giving such directions," is early 15c. Related: Instructions.
insubordinate (adj.): 1792, on model of French insubordonné (1787); from in- (1) "not, opposite of" + subordinate (adj.) "submitting to authority." Related: Insubordinately.
insufferable (adj.): "intolerable, not to be endured," early 15c., from in- (1) "not, opposite of" + sufferable. Related: Insufferably.