Online Etymology Dictionary

ignore (v.): 1610s, "not to know, to be ignorant of," from French ignorer "be unaware of" (14c.), or directly from Latin ignorare "not to know, be unacquainted; take no notice of, disregard" (see ignorant). The original sense in English is obsolete. Sense of "pass over without notice, pay no attention to" in English first recorded 1801 (Barnhart says "probably a dictionary word"), and OED indicates it was uncommon before c. 1850. Related: Ignored; ignoring.
iguana (n.): large lizard of the American tropics, 1550s, from Spanish, from Arawakan (W.Indies) iguana, iwana, the local name for the lizard.
Foure footed beastes ... named Iuannas, muche lyke vnto Crocodiles, of eyght foote length, of moste pleasaunte taste. [Richard Eden, "Decades of the New World," 1555]
iguanodon (n.): dinosaur name, 1825, hybrid from iguana + Latinized stem of Greek odonys "tooth" (on model of mastodon). So called because the fossil teeth and bones were thought to resemble (except in size) those of the tropical lizard.
ikebana (n.): Japanese are of formal flower arrangement, 1901, from Japanese, from ikeru "to keep alive, arrange" + hana "flower."
il-: assimilated form of Latin prefix in- used with words beginning in l-; see in-.
ileo-: word-forming element, from comb. form of ileum (q.v.).
ileum (n.): lowest part of the small intestine, 1680s, medical Latin, from ileum, in medieval medicine "the part of the small intestines in the region of the flank," singular created from Latin ilia (pl.) "groin, flank," in classical Latin, "belly, the abdomen below the ribs," poetically, "entrails, guts." The word apparently was confused in Latin with Greek eileos "colic" (see ileus), or perhaps is a borrowing of it. The sense is "winding, turning," either via the Greek meaning or from the convolutions of the intestines. Earlier in English ylioun (late 14c.), from Medieval Latin ileon. Related: Ileitis; ileal.
ileus (n.): painful intestinal condition, 1706, from Latin ileus "severe colic," from Greek eileos "colic," from eilein "to turn, squeeze," from PIE *wel- (3) "to turn, roll" (see volvox).
ilex (n.): "evergreen oak," late 14c., from Latin ilex "holm-oak, great scarlet oak," perhaps from an extinct non-Indo-European language.
ilia: Latin plural of ilium (see ileum).
iliac (adj.): 1510s, "pertaining to colic," from Middle French iliaque (16c.) or directly from Late Latin iliacus, from ileus "severe colic" (see ileus).
Iliad: from Latin Ilias (genitive Iliadis), from Greek Ilias poiesis "poem of Ilion" (Troy), literally "city of Ilius," the mythical founder. With -ad.
ilium (n.): pelvic bone, 1706, Modern Latin, from Latin ilia (plural) "groin, flank, side of the body from the hips to the groin" (see ileum). In Middle English it meant "lower part of the small intestine." Vesalius gave the name os ilium to the "bone of the flank."
Ilium: "Troy;" see Iliad.
ilk (adj.): Old English ilca "the same" (pron.), from Proto-Germanic *ij-lik (compare German eilen), in which the first element is from the PIE demonstrative particle *i- (see yon) and the second is that in Old English -lic "form" (see like (adj.)). Of similar formation are each, which and such, but this word disappeared except in Scottish and thus did not undergo the usual southern sound changes. Phrase of that ilk implies coincidence of name and estate, as in Lundie of Lundie; it was applied usually to families, so that by c. 1790 ilk began to be used with the meaning "family," then broadening to "type, sort."
ill (adj.): c. 1200, "morally evil; offensive, objectionable" (other 13c. senses were "malevolent, hurtful, unfortunate, difficult"), from Old Norse illr "evil, bad; hard, difficult; mean, stingy," a word of unknown origin. Not considered to be related to evil. From mid-14c. as "marked by evil intentions; harmful, pernicious." Sense of "sick, unhealthy, diseased, unwell" is first recorded mid-15c., probably from a use similar to that in the Old Norse idiom "it is bad to me." Slang inverted sense of "very good, cool" is 1980s..
ill (v.): early 13c., "do evil to," from ill (adj.). Meaning "speak disparagingly" is from 1520s. Related: Illed; illing.
ill (adv.): c. 1200, "wickedly; with hostility," from ill (adj.). Meaning "not well, poorly" also is from c. 1200. It generally has not shifted to the realm of physical sickness, as the adjective has done. Ill-fated recorded from 1710; ill-informed from 1824; ill-tempered from c. 1600; ill-starred from c. 1600. Generally contrasted with well, hence the useful, but now obsolete or obscure illcome (1570s), illfare (c. 1300), and illth.
ill-advised (adj.): 1590s, from ill (adv.) + advise (v.). Related: Ill-advisedly.
ill-bred (adj.): 1620s, from ill (adv.) + bred (adj.).
ill-fated (adj.): 1710 (Pope), from ill (adv.) + fated.
ill-favored (adj.): of persons, "ugly," 1520s, from ill (adv.) + favored (q.v.).
ill-gotten (adj.): 1550s, from ill (adv.) + gotten.
ill-mannered (adj.): early 15c., from ill (adv.) + mannered.
ill-timed (adj.): 1690s, from ill (adv.) + time (v.).
illative (adj.): 1610s, "stating or introducing an inference" (of words such as because, then, therefore); 1630s, "inferential, arising from inference," from Late Latin illativus, from Latin illatus "brought in," used as past participle of inferre "to bring in, introduce" (see infer). Grammatical sense "case expressing motion into" is from 1890. As a noun from 1590s, "illative word." Related: Illation "action of inferring" (1530s).
illegal (adj.): 1630s, from French illégal (14c.) or directly from Medieval Latin illegalis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin legalis (see legal). Term illegal immigrant first recorded 1892 in American English (illegal immigration is from 1887); used in British English in 1940s in reference to the Jewish movement to Palestine.
illegality (n.): quality of being illegal," 1630s, from illegal (adj.) + -ity; or else from French illegalité (14c.).
illegally (adv.): 1620s, from illegal (adj.) + -ly (2).
illegible (adj.): 1630s, from assimilated form of in- (1) "not, opposite of" + legible. Related: Illegibly; illegibility.
illegitimacy (n.): 1670s; see illegitimate + -acy.
illegitimate (adj.): 1530s, "born out of wedlock," formed in English (and replacing earlier illegitime, c. 1500), modeled on Late Latin illegitimus "not legitimate" (see il- + legitimate). Sense of "unauthorized, unwarranted" is from 1640s. Phrase illegitimi non carborundum, usually "translated" as "don't let the bastards grind you down," is fake Latin (by 1965, said to date from c. 1939). Carborundum was a brand of abrasives. Related: Illegitimately.
illiberal (adj.): 1530s, "ungentlemanly, base, mean," from Middle French illiberal (14c.), from Latin illiberalis "ungenerous, mean, sordid; unworthy of a freeman; stingy, disobliging," from assimilated form of in- "not, opposite of" (see in- (1)) + liberalis (see liberal (adj.)). A sense of "narrow-minded politically; unconcerned with the rights or liberties of others" is attested from 1640s (as a noun in this sense 1818), and might be revived to ease the load of meanings that weighs on conservative.
illicit (adj.): c. 1500, from Old French illicite "unlawful, forbidden" (14c.), from Latin illicitus "not allowed, unlawful, illegal," from assimilated form of in- "not, opposite of" (see in- (1)) + licitus "lawful," past participle of licere "to be allowed" (see licence (n.)). Related: Illicitly.
illimitable (adj.): 1590s, from assimilated form of in- (1) "not" + limitable.
illing (n.): "evil-doing, malevolent treatment," early 13c., verbal noun from ill (v.).
Illinois: 1703, in reference to the language, from the name of a native Algonquian people who called themselves Inoca (1725), also written Ilinouek, Old Ottawa for "ordinary speaker." The modern form represents a 17c. French spelling, pronounced "ilinwe" at that time. The U.S. territory was created 1809, admitted as a state 1818. Related: Illinoisan (1836), which seems to be the usual form; Illinoian is used in geology to refer to one of the Pleistocene ice ages in North America (1896) and earlier it was a newspaper name (1838) and a steamboat (1837). Illinoisian (adj.) was used in England in 1818.
illiquid (adj.): 1690s, from assimilated form of in- (1) "not" + liquid (adj.) in the financial sense.
illiteracy (n.): 1650s, "inability to read and write," from illiterate + -cy. Earlier in this sense was illiterature (1590s).
illiterate (adj.): early 15c., "uneducated, unable to read and write" (originally meaning Latin), from Latin illiteratus "unlearned, unlettered, ignorant; without culture, inelegant," from assimilated form of in- "not, opposite of" (see in- (1)) + literatus "educated," literally "furnished with letters" (see literate). Rendered in Old English as unstæfwis. As a noun meaning "illiterate person" from 1620s. Hence, illiterati (1788, Horace Walpole).
illness (n.): "disease, sickness, ailment, malady," 1680s, from ill (adj.) + -ness. Earlier it meant "bad moral quality" (c. 1500).
illocution (n.): 1955, from assimilated form of in- (1) "not, opposite of" + locution.
illocutionary (adj.): 1955, from illocution + -ary.
illogical (adj.): "without sound reasoning according to rules of logic," 1580s, from assimilated form of in- (1) "not, opposite of" + logical. Related: Illogically.
illth (n.): "what leads one to a bad state or condition," 1867, coined by John Ruskin from ill (adv.) on model of wealth (also see -th (2)).
[S]uch things, and so much of them as he can use, are, indeed, well for him, or Wealth; and more of them, or any other things, are ill for him, or Illth. [Ruskin, "Munera Pulveris"]
illude (v.): early 15c., to trick, deceive; treat with scorn or mockery," from Latin illudere "to make sport of, scoff at, mock, jeer at," from assimilated form of in- "in, into" (see in- (2)) + ludere "to play" (see ludicrous).
illume (v.): "illuminate," c. 1600, from French illumer, contraction of illuminer, from Latin illuminare "light up, make light, illuminate" (see illumination). Related: Illumined; illumining.
illuminate (v.): c. 1500, "to light up, shine on," a back-formation from illumination or else from Latin illuminatus, past participle of illuminare "light up, make light, illuminate." Earlier was enlumyen (late 14c.) "decorate written material by hand with gold, silver, or bright colors," from Old French enluminer, from Late Latin inluminare; also illumine (late 14c.). Related: Illuminated; illuminating; illuminable.
illuminati (n.): 1590s, plural of Latin illuminatus "enlightened" (in figurative sense), past participle of illuminare "light up, make light, illuminate" (see illumination). Originally a name applied to a 16c. Spanish sect (the Alumbrados), then to other sects on the continent; since 1797 used as a translation of German Illuminaten, name of a secret society founded 1776 in Ingolstadt, Bavaria, (repressed there 1785) and holding deistic and republican principles; hence used generally of free-thinkers and sarcastically of those professing intellectual enlightenment (1816). Related: Illuminatism; illuminatist.
illumination (n.): late 14c., "spiritual enlightenment," from Late Latin illuminationem (nominative illuminatio), noun of action from past participle stem of Latin illuminare "to throw into light, make bright, light up;" figuratively, in rhetoric, "to set off, illustrate," from assimilated form of in- "in, into" (see in- (2)) + lumen (genitive luminis) "light," related to lucere "to shine" (see light (n.)). Meaning "action of lighting" in English is from 1560s; sense of "intellectual enlightenment" is from 1630s.