Online Etymology Dictionary

inlay (v.): 1590s, "insert in or into," from in (adv.) + lay (v.). As a noun, "that which is inlaid" (especially for ornamental effect), from 1650s. Related: Inlaid.
in-house (adj.): also inhouse, 1955, from in (prep.) + house (n.).
inhalant (adj.): 1804, from Latin inhalantem, present participle of inhalare (see inhale). As a noun from 1830.
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" (see in- (2)) + halare "breathe."
inline (adj.): also in-line, 1913 of printing, 1921 of engines, 1958 of computers, by 1989 of roller skates; from in + line (n.).
innermost (adj.): mid-14c., from inner + -most. In the same sense innerest is from c. 1200. The older word is inmost. Innermore also existed in Middle English.
innocence (n.): mid-14c., "freedom from guilt or moral wrong," from Old French inocence "innocence; purity, chastity" (12c., Modern French innocence), from Latin innocentia "blamelessness, uprightness, integrity," from innocens "harmless; blameless; disinterested" (see innocent). Meaning "lacking in guile or artifice," as of childhood, is from late 14c. Meaning "freedom from legal wrong" is from 1550s.
innocense (n.): alternative spelling of innocence.
inhibitory (adj.): late 15c., from Medieval Latin inhibitorius "inhibitory," from inhibit-, past participle stem of Latin inhibere "to hold in, keep back" (see inhibition).
inhibitor (n.): 1868 as a Scottish legal term; 1914 in biochemistry; agent noun in Latin form from inhibit. Form inhibiter is attested from 1610s.
inhance (v.): obsolete form of enhance. Related: Inhancement.
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.
inherence (n.): 1570s, from Middle French inhérence (15c.) or directly from Medieval Latin inhaerentia, from inhaerentem (see inherent). Related: Inherency (c. 1600).
inoculation (n.): mid-15c. in horticulture, "act or practice of grafting buds;" 1714 in pathology, "insertion of a form of a virus in order to prevent a more serious attack of it," 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 (adj.). Related: Inoffensively; inoffensiveness.
inoperable (adj.): "incapable of being treated by surgical operation," 1856, from in- (1) "not, opposite of" + operable.
inoperative (adj.): "not working," 1630s, from in- (1) "not, opposite of" + operative (adj.).
inorganic (adj.): 1727, "without the organized structure which characterizes living things," from in- (1) "not, opposite of" + organic (adj.). Inorganical in this sense is from 1670s. Meaning "not arriving by natural growth" is recorded from 1862.
insecurity (n.): 1640s, "state of being unsafe," also "lack of assurance or confidence, apprehension," from Medieval Latin insecuritas, from insecurus (see insecure). Specific psychological sense is by 1917.
insectivore (n.): 1863, from French insectivore (1817), from Latin insectivorus, from comb. form of insectum (see insect) + vorare "devour, swallow" (see voracity).
insense (v.): "teach, instruct, cause (someone) to understand," c. 1400, ensense, from Old French ensenser "to enlighten, to bring to sense," from en- "in" (see in- (2)) + sens (see sense (n.)). "From 17th c. app. only dialectal (chiefly northern), or in writers under dialectal influence" [OED].
insertion (n.): 1590s, "act of putting in," from French insertion (16c.) or directly from Late Latin insertionem (nominative insertio) "a putting in," noun of action from past participle stem of Latin inserere "to graft, implant" (see insert (v.)). Meaning "that which is inserted" attested from 1620s.
in-service (adj.): also inservice, 1928, from in (prep.) + service (n.).
insider (n.): "one in possession of special information by virtue of being within some organization," 1848, from inside (n.) + -er (1). Originally in reference to the stock markets.
inscribe (v.): 1550s, "to write on or in" (something durable and conspicuous), from Latin inscribere "to write in or on," (see inscription). Meaning "to dedicate (by means of an inscription)" is from 1640s. Form inscriven is from late 14c. Related: Inscribed; inscribing.
insatiate (adj.): "not to be satisfied," mid-15c., insaciate, from Latin insatiatus "unsatisfied," from in- "not, opposite of" (see in- (1)) + satiatus, past participle of satiare "to fill, satisfy" (see satiate).
insalubrious (adj.): 1630s, from Latin insalubris "unhealthy, unwholesome," or else a native formation from in- (1) "not, opposite of" + salubrious. Related: Insalubriety.
inpatient (n.): also in-patient, "patient lodged and fed, as well as treated, at a hospital or infirmary," 1760, from in (adj.) + patient (n.). As an adjective from 1959.
inquisitor (n.): c. 1400, "an inspector, one who makes inquiries," from Anglo-French inquisitour, Old French inquisiteur, or directly from Latin inquisitor "searcher, examiner; a legal investigator, collector of evidence," agent noun from Latin inquirere (see inquire). As the title of an officer of the Inquisition, from 1540s. Related: Inquisitorial. Of the fem. forms, inquisitress (1727) is senior to inquisitrix (1825).
insignificance (n.): 1690s, from insignificant + -ance. Earlier was insignificancy (1650s).
insincerity (n.): 1540s, from in- (1) "not, opposite of" + sincerity, or else from Latin insincerus "not genuine, not pure; spoiled, corrupted" (see insincere).
insinuation (n.): 1520s, "act of making an indirect suggestion;" 1530s, "that which is indirectly suggested," from Middle French insinuation (16c.) or directly from Latin insinuationem (nominative insinuatio) "entrance through a narrow way; an ingratiating oneself," noun of action from past participle stem of insinuare "creep in, intrude, wind one's way into" (see insinuate).
insistence (n.): mid-15c., "persistence, urgency," from Old French insister "to insist" (14c.) and directly from Latin insistere (see insist) + -ence.
inspect (v.): 1620s, from Latin inspectus, past participle of inspicere "look at, observe, view; look into, inspect, examine," from in- "into" (see in- (2)) + specere "to look" (see scope (n.1)). Related: Inspected; inspecting.
inspector (n.): c. 1600, "overseer, superintendent," from Latin inspector "one who views or observes," agent noun 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)). As a police ranking between sergeant and superintendent, it dates from 1840. Related: Inspectorial (1752). Of the 18c. feminine formations, inspectrix (1703) is earlier than inspectress (1737).
inspissate (v.): "make thick or thicker," 1620s, from Late Latin inspissatus, past participle of inspissare, from in- "in, into" (see in- (2)) + Latin spissare "to thicken," related to spissus "thick" (see spissitude). Related: Inspissated; inspissating.
insolvency (n.): 1660s, from insolvent (q.v.) + -cy. Insolvence (1793) is rare.
insolate (v.): "expose to the rays of the sun," 1620s, from Latin insolatus, past participle of insolare "place in the sun, expose to the sun," from in- "in" (see in- (2)) + sol "sun" (see Sol). Related: Insolated; insolating.
insole (n.): "inner sole of a shoe or boot," 1838, from in + sole (n.1).
insistent (adj.): 1620s, "standing on something," from Latin insistentem (nominative insistens), present participle of insistere "stand on," also "urge, insist," from in- "upon" (see in- (2)) + sistere "take a stand" (see assist (v.)). Meaning "persistent, urgent, demanding attention" is from 1868. Related: Insistently.
i'nt: also i'n't, 18c., contraction representing a casual pronunciation of isn't it.
intaglio (n.): "incised engraving" (as opposed to carving in relief), 1640s, from Italian intaglio "engraved work" (plural intagli), from intagliare "to cut in, engrave," from in- "in" (see in- (2)) + tagliare "to cut," from Late Latin taliare "to split" (see tailor (n.)).
intail (v.): obsolete form of entail. Related: Intailed; intailing.
integumentary (adj.): 1826, from integument + -ary.
intellectualism (n.): 1818, in philosophy, "belief in the supremacy of the intellect," probably based on German Intellektualismus (said by Klein to have been coined 1803 by Friedrich Wilhelm Joseph von Schelling (1775-1854) from Late Latin intellectualis); see intellectual + -ism. Meaning "devotion to intellectuality" also is from 1818.
insurgence (n.): 1776; see insurgent + -ence. Perhaps from French insurgence (by 1740s).
insurgency (n.): 1798, from insurgent + -cy.
insurer (n.): 1650s, agent noun from insure (v.).
insulator (n.): 1801, agent noun in Latin form from insulate (v.). In reference to the glass or earthenware devices to hold telegraph (later telephone) wires, from 1840s.
insulation (n.): noun of action from insulate (v.) in its various senses. From 1767 as "a blocking from electricity or heat" (by interposition of a non-conductor). Sense of "state or action of being detached from others" is from 1798. Literal meaning "act of making (land) into an island" is from 1784; that of "state of being an island" is from 1799. The concrete sense of "insulating material" is recorded by 1870.