Online Etymology Dictionary

inlay: 1590s (v.), 1650s (n.), from in + lay. Related: Inlaid.
inlet (n.): 1570s, "narrow opening into a coast, arm of the sea," a special use of Middle English inleten "to let in" (c.1300), from in + let (v.). In this sense said by old sources to be originally a Kentish term.
inline: 1923 of printing, 1929 of engines, 1958 of computers, by 1989 of roller skates; from in + line.
inly (adv.): Old English inlice "internally; sincerely;" see in + -ly (2).
inmate (n.): 1580s, "one allowed to live in a house rented by another" (usually for a consideration), from in "inside" + mate "companion." Sense of "one confined to an institution" is first attested 1834.
inmost: Old English innemest; see in + -most.
inn (n.): Old English inn "lodging, dwelling, house," probably from inne (adv.) "inside, within" (see in). Meaning "public house with lodging" is perhaps by c.1200, certainly by c.1400. Meaning "lodging house or residence for students" is early 13c. in Anglo-Latin, obsolete except in names of buildings that were so used (e.g. Inns of Court, mid-15c.).
innards (n.): 1825, innerds, dialectal variant of inwards "the bowels" (c.1300); see inward.
innate (adj.): early 15c., from Late Latin innatus "inborn," past participle of innasci "to be born in, originate in," from in- "in" (see in- (2)) + nasci "to be born" (Old Latin gnasci; see genus). Related: Innately.
inner (adj.): c.1400, from Old English inra, comp. of inne (adv.) "inside" (see in). Cf. Old High German innaro, German inner. An unusual evolution for a comparative, it has not been used with than since Middle English. Inner tube in the pneumatic tire sense is from 1894. Inner city, in reference to poverty and crime, is attested from 1968.
innermost: mid-14c., from inner + -most. Innermore also existed in Middle English.
innervate (v.): 1870, from in- (2) "in" + Latin nervus (see nerve) + -ate. Probably rather a back-formation from innervation (1832). Related: Innervated. Innervation in psychology is from 1880.
innie (n.): in reference to navels, by 1972, from in (adv.) + -ie.
inning (n.): Old English innung "a taking in, a putting in," gerundive of innian "get within, put or bring in," from inn (adv.) "in" (see in). Meaning "a team's turn in a game" first recorded 1735, usually plural in cricket, singular in baseball.
innkeeper (n.): 1540s, from inn + keeper.
innocence (n.): mid-14c., "freedom from guilt," from Old French inocence "innocence, purity, chastity" (12c.), from Latin innocentia, from innocens "harmless, blameless" (see innocent). Meaning "lacking in guile or artifice" is from late 14c.
innocense (n.): alternative spelling of innocence.
innocent (adj.): mid-14c., "doing no evil, free from sin or guilt," from Old French inocent "harmless; not guilty; pure" (11c.), from Latin innocentem (nominative innocens) "not guilty, harmless, blameless," from in- "not" (see in- (1)) + nocentem (nominative nocens), present participle of nocere "to harm" (see noxious). Meaning "free from guilt of a specific crime or charge" is from late 14c. The earliest use was as a noun, "person who is innocent of sin or evil" (c.1200). The Holy Innocents (early 14c.) were the young children slain by Herod sfter the birth of Jesus (Matt. ii:16).
innocently (adv.): c.1400, from innocent (adj.) + -ly (2).
innocuous (adj.): 1590s, from Latin innocuus "harmless," from in- "not" (see in- (1)) + nocuus "hurtful," from root of nocere "to injure, harm," from *nok-s-, suffixed form of PIE root *nek- "death" (see necro-). Related: Innocuously; innocuousness.
innovate (v.): 1540s, "introduce as new," from Latin innovatus, past participle of innovare "to renew, restore; to change," from in- "into" (see in- (2)) + novus "new" (see new). Meaning "make changes in something established" is from 1590s. Related: Innovated; innovating.
innovation (n.): mid-15c., "restoration, renewal," from Latin innovationem (nominative innovatio), noun of action from past participle stem of innovare (see innovate).
innovative (adj.): 1806 (with an isolated use from c.1600), from innovate + -ive. Related: Innovatively; innovativeness.
innovator (n.): 1590s, from Late Latin innovator, agent noun from innovare (see innovate).
innuendo (n.): 1670s, "oblique hint, indiscreet suggestion," usually a depreciatory one, from Latin innuendo "by meaning, pointing to," literally "giving a nod to," ablative of gerund of innuere "to mean, signify," literally "to nod to," from in- "at" + nuere "to nod" (see numinous). Originally a legal phrase (1560s) from Medieval Latin, with the sense of "to wit." It often introduced the derogatory meaning alleged in libel cases, which influenced its broader meaning. As a verb, from 1706.
Innuit: 1765, from Inupiaq Eskimo inuit "people," plural of inuk "man, person."
innumerable (adj.): mid-14c., from Latin innumerabilis "countless, immeasurable," from in- "not" (see in- (1)) + numerabilis "able to be numbered," from numerare "to count, number," from numerus "a number" (see number (n.)).
inobservant (adj.): 1660s, from Latin inobservantem (nominative inobservans) "inattentive, negligent," from in- "not" (see in- (1)) + observans (see observance).
inoculate (v.): mid-15c., "implant a bud into a plant," from Latin inoculatus, past participle of inoculare "graft in, implant," from in- "in" (see in- (2)) + oculus "bud," originally "eye" (see eye (n.)). Meaning "implant germs of a disease to produce immunity" first recorded (in inoculation) 1714, originally in reference to smallpox. After 1799, often used in sense of "to vaccine inoculate." Related: Inoculated; inoculating.
inoculation (n.): mid-15c. in horticulture; 1714 in pathology, from Latin inoculationem (nominative inoculatio) "an engrafting, budding," noun of action from past participle stem of inoculare (see inoculate).
inoffensive (adj.): 1590s, from in- (1) "not, opposite of" + offensive. Related: Inoffensively; inoffensiveness.
inoperable (adj.): 1856, from in- (1) "not, opposite of" + operable.
inoperative (adj.): 1630s, from in- (1) "not, opposite of" + operative.
inopportune (adj.): 1530s, from Late Latin inopportunus "unfitting," from in- "not" + opportunus (see opportune). A rare word before 19c. Related: Inopportunely.
inordinate (adj.): late 14c., "not ordered, lacking order or regularity," from Latin inordinatus "unordered, not arranged," from in- "not, opposite of" (see in- (1)) + ordinatus, past participle of ordinare "to set in order" (see order). Sense of "immoderate, excessive" is from notion of "not kept within orderly limits." Related: Inordinately; inordinateness.
inorganic (adj.): 1794, "without organized organic structure," from in- (1) "not, opposite of" + organic. Sense of "not arriving by natural growth" recorded from 1862.
inpatient: 1760 (n.); 1959 (adj.), from in + patient.
input (n.): 1793, "a sum (of cash) put in," from in + put. Computing sense of "data fed into a machine" is from 1948; the verb in the computing sense is attested from 1946. There was a Middle English verb input (late 14c.) meaning "to put in, place, set," but it died out long before this.
inquest (n.): late 13c., an-queste "legal or judicial inquiry," from Old French enqueste "inquiry," from Vulgar Latin *inquaestia (cf. Italian inchiesta), from fem. past participle of Vulgar Latin *inquirere "inquire" (see inquire).
inquire (v.): late 13c., from Old French enquerre "ask, inquire about" (Modern French enquérir), from Vulgar Latin *inquaerere, from Latin in- "into" (see in- (2)) + quaerere "ask, seek" (see query (v.)). Respelled 14c. on Latin model, but half-Latinized enquire still persists. Related: Inquired; inquiring; inquiringly.
inquirer (n.): 1560s, "one who inquires," agent noun from inquire.
inquiry (n.): mid-15c., enquery, from enquere (see inquire). Respelled from mid-16c. to conform to Latin.
inquisition (n.): late 14c., "judicial investigation, act or process of inquiring," from Old French inquisicion "inquiry, investigation" (12c.), from Latin inquisitionem (nominative inquisitio) "a searching into, legal examination," 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, and the Inquisition refers to the ecclesiastical court (Congregation of the Holy Office) appointed 13c. by Innocent III to suppress heresy. It never operated in Britain. The capital letter form appeared in English only after c.1500, and usually refers to the office's reorganization 1478-1483 in Spain as what is commonly called the Spanish Inquisition.
inquisitive (adj.): late 14c., from Old French inquisitif, from Late Latin inquisitivus "making inquiry," from Latin inquisit-, past participle stem of inquirere (see inquire).
An housbonde shal nat been Inquisityf of goddes pryuetee nor of his wyf. [Chaucer, "Miller's Prologue"]
Related: Inquisitively; inquisitiveness.
inquisitor (n.): c.1400, from Old French inquisiteur (c.1400) or directly from Latin inquisitor "searcher, examiner," in law, "an investigator, collector of evidence," agent noun from Latin inquirere (see inquire). As the title of an officer of the Inquisition, from 1540s. Related: Inquisitorial.
inro: 1610s, from Japanese, from Chinese yin "seal" + lung "basket."
inroad (n.): 1540s, "hostile incursion, raid, foray," from in- (2) "in;" second element is road in the obsolete sense of "riding;" related to raid. Related: Inroads.
insalubrious (adj.): 1630s, from Latin insalubris "unhealthy, unwholesome," from in- "not" (see in- (1)) + salubris (see salubrious).
insane (adj.): 1550s, from Latin insanus "mad, insane; outrageous, excessive, extravagant," from in- "not" (see in- (1)) + sanus "well, healthy, sane." Originally only of persons; of actions, from 1842. Cf. 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]. The noun meaning "insane person" is attested from 1786.
insanity (n.): 1580s, "state of being insane," from Latin insanitatem (nominative insanitas) "unhealthfulness," noun of quality from insanus (see insane). Meaning "extreme folly" is from 1844.