Online Etymology Dictionary

intersect (n.): "point of intersection," 1850, from intersect (v.) or from Latin intersectum, neuter past pasticiple of intersecare. Earlier (1650s) it was used for "an insect."
interspersion (n.): 1650s, noun of action from intersperse.
inter-war (adj.): 1939, in reference to the period between the world wars, from inter- + war (n.).
intimidation (n.): 1650s, noun of action from intimidate; perhaps modeled on French intimidation (16c.).
intolerability (n.): 1590s, from intolerable + -ity or else from Late Latin intolerabilitas, from Latin intolerabilis "that cannot bear; that cannot be borne." Slightly earlier in the same sense was intolerableness.
intoxicated (adj.): 1550s, "poisoned;" 1570s, "drunk," past participle adjective from intoxicate (v.).
intractability (n.): 1570s, from intractable + -ity. Intractableness is from 1660s.
intransigence (n.): 1874, from intransigent or else from or based on French intransigeance, from intransigent. Related: Intransigency (1883).
in-transit (adj.): 1907, from commercial verbal phrase in transit "on the way or passage, while passing from one to another" (1819, earlier in Latin form in transitu), from in + transit (n.).
intrepidity (n.): 1640s, from intrepid (adj.) + -ity.
intrigante (n.): also intriguante, "woman given to intrigue," 1806, from fem. of French intrigant "male intriguer," from Italian intrigante, noun use of present participle of intrigare "to plot, meddle" (see intrigue (v.)).
introject (v.): 1902 in psychology, probably a back-formation from introjection. Related: Introjected; introjecting.
inutility (n.): 1590s, from Middle French inutilité (15c.), from Latin inutilitas "uselessness," from inutilis "useless, unprofitable," from in- "not" (see in- (1)) + utilis "useful, beneficial, profitable," from uti "make use of, profit by, take advantage of" (see use (v.)).
intumescence (n.): "swollen state, expansion," 1650s, from French intumescence (17c.), from Latin intumescere "to swell up, rise, be elevated," of sounds, "grow louder," figuratively, "grow excited, become enraged," from in- "in" (see in- (2)) + tumescere "begin to swell, swell up" (see tumescence).
invalidation (n.): 1752, noun of action from invalidate (v.). Perhaps modeled on French invalidation (17c.).
invalidity (n.): 1540s, from Middle French invalidité (16c.) or directly from Medieval Latin invaliditas "weakness, infirmity," from Latin invalidus "not strong, weak, feeble" (see invalid (adj.1)).
invariability (n.): 1640s, from invariable + -ity. Invariableness is from 1650s.
invigoration (n.): 1660s, noun of action from invigorate. Perhaps modeled on French invigoration.
invincibility (n.): 1670s, from invincible + -ity. Invincibleness is recorded from 1610s.
inviolability (n.): 1660s, from inviolable + -ity.
investor (n.): 1580s, "one who clothes;" 1862, "one who invests money," agent noun from invest.
invisibility (n.): 1560s, from Late Latin invisibilitas, from Latin invisibilis "not visible, unseen" (see invisible).
invite (n.): "an invitation," 1650s, from invite (v.).
inwardly (adv.): Old English inweardlice; see inward + -ly (2).
involvement (n.): 1706, from involve + -ment.
invulnerability (n.): 1707, from invulnerable + -ity.
inwardness (n.): late 14c., from inward + -ness.
invita Minerva: Latin adverbial phrase, used with reference to literary or artistic creation, "without inspiration," literally "Minerva unwilling;" i.e. "without inspiration from the goddess of wisdom;" ablative fem. of invitus "against the will, unwilling, reluctant," according to de Vaan from PIE compound *n-uih-to- "not turned to, not pursuing," related to the source of invitation. With Minervā, ablative absolute of Minerva.
interview (v.): in early use also enterview, enterveu, 1540s, "to have a personal meeting," from interview (n.). Meaning "have an interview with" (usually with intent to publish what is said" is from 1869. Related: Interviewed; interviewing.
interviewee (n.): 1883, from interview (v.) + -ee.
interviewer (n.): 1868, in the journalistic sense, agent noun from interview (v.).
intimate (n.): 1650s, "familiar friend, person with whom one is intimate," from intimate (adj.). Sometimes 17c.-19c. in false Spanish form intimado. Latin intimus had a similar noun sense. Intimates as a commercial euphemism for "women's underwear" is from 1988.
intrigue (n.): 1640s, "a clandestine plot;" 1660s, "secret plotting," probably from intrigue (v.). Also used from 1660s as "clandestine or illicit sexual encounter."
invalid (n.): "infirm or sickly person," 1709, originally of disabled military men, from invalid (adj.1). In Paris, Invalides is short for Hôtel des Invalides, home for old and disabled soldiers in the 7th arrondissement of Paris.
invalid (adj.2): "of no legal force," 1630s, from special use of Latin invalidus "not strong, weak, feeble" (see invalid (adj.1)).
invigilator (n.): 1890, agent noun from invigilate.
invigorating (adj.): 1690s, adjective from present participle of invigorate. Related: Invigoratingly.
inviting (adj.): "attractive, alluring," c. 1600, present-participle adjective from invite (v.). Related: Invitingly.
involved (adj.): "complicated," 1640s, past participle adjective from involve. Earlier it meant "spirally curved" (1610s).
iodize (v.): "add iodine to, treat with iodine," 1841, from iodine + -ize. Related: Iodized; iodizing.
iodide (n.): compound of iodine, 1822, from iod-, comb. form of iodine used before vowels + -ide.
ionic (adj.): "pertaining to ions," 1890, from ion + -ic.
Iranian (adj.): 1788, "of or pertaining to (ancient) Persia," from Iran + -ian. From 1839 in reference to the language. As a noun, "an inhabitant of Persia" (1792), later "the language of Persia" (1850). Iranic (adj.) is from 1847.
irascibility (n.): 1701, from irascible + -ity.
irenology (n.): "study of peace," 1974, from Greek eirene "peace" + -ology. Related: Irenological.
irradicable (adj.): "that cannot be rooted out," 1728, from assimilated form of in- (1) "not, opposite of" + radicable, from Latin radix "root" (see radish), Latin radicare meant "to take root," and English irradicate (v.) means both "root out" (1709) and "to root, fix by the root" (1660s).
irony (adj.): "of or resembling iron," late 14c., from iron (n.) + -y (2).
iron-gray (adj.): Middle English, from Old English isengræg; see iron (n.) + gray (adj.). The color of freshly broken cast iron.
iron-on (adj.): 1959, from the verbal phrase, from iron (v.) + on (adv.).
iron (v.): c. 1400, irenen, "to make of iron," from iron (n.). Meaning "shackle with irons" is from 1650s. Meaning "press clothes" (with a heated flat-iron) is recorded from 1670s. Related: Ironed; ironing.