Online Etymology Dictionary

iodize: 1841, from comb. form of iodine + -ize. Related: Iodized; iodizing.
ion (n.): 1834, introduced by English physicist and chemist Michael Faraday (suggested by the Rev. William Whewell, English polymath), coined from Greek ion, neuter present participle of ienai "go," from PIE root *ei- "to go, to walk" (cf. Greek eimi "I go;" Latin ire "to go," iter "a way;" Old Irish ethaim "I go;" Irish bothar "a road" (from *bou-itro- "cows' way"), Gaulish eimu "we go," Gothic iddja "went," Sanskrit e'ti "goes," imas "we go," ayanam "a going, way;" Avestan ae'iti "goes;" Old Persian aitiy "goes;" Lithuanian eiti "to go;" Old Church Slavonic iti "go;" Bulgarian ida "I go;" Russian idti "to go"). So called because ions move toward the electrode of opposite charge.
Ionian (adj.): "of Ionia," the districts of ancient Greece inhabited by the Ionians (including Attica and the north coast of the Peloponnesus, but especially the coastal strip of Asia Minor, including the islands of Samos and Chios). The name (which Herodotus credits to an ancestral Ion, son of Apollo and Creusa) probably is pre-Greek, perhaps related to Sanskrit yoni "womb, vulva," and a reference to goddess-worshipping people.

Also used of the sea that lies between Italy and the northern Peloponnesus (1630s). The musical Ionian mode (1844) corresponds to our basic major scale but was characterized by the Greeks as soft and effeminate, as were the Ionians generally.
The Ionians delighted in wanton dances and songs more than the rest of the Greeks ... and wanton gestures were proverbially termed Ionic motions. [Thomas Robinson, "Archæologica Græca," 1807]
Ionic: "pertaining to Ionia," 1570s of music; 1580s of architecture, from Latin Ionicus, from Greek Ionikos (see Ionian).
ionic: "pertaining to ions," 1890, from ion + -ic.
ionization: 1891; see ionize + -ation.
ionize: 1896, from ion + -ize. Related: Ionized; ionizing.
ionosphere: 1926, from ion + sphere. Coined by Scottish radar pioneer Robert A. Watson-Watt (1892-1973). So called because it contains many ions.
iota: "very small amount," 1630s, figurative use of iota, ninth and smallest letter in the Greek alphabet. Modern use is after Matt. v:18 (see jot), but iota in classical Greek also was proverbially used of anything very small. The letter name is from Semitic (cf. Hebrew yodh).
Iowa: organized as a U.S. territory 1838; admitted as a state 1846, ultimately from the name of the native people, of the Chiwere branch of the Aiouan family; said to be from Dakota ayuxba "sleepy ones."
ipecac: 1710, borrowing via Portuguese of a shortened form of Tupi ipecacuana (a word attested in English from 1682), a medicinal plant of Brazil. The Indian word is said to mean "small plant causing vomit."
ipse dixit: Latin, literally "he (the master) said it," translation of Greek autos epha, phrase used by disciples of Pythagoras when quoting their master.
ipseity (n.): 1650s, from Latin ipse "self" + -ity.
ipsilateral (adj.): 1907, from Latin ipse "self" + lateral.
ipso facto: Latin, literally "by that very fact."
ir-: assimilated form of Latin prefixes in- (see in-) before -r-.
Ira: masc. proper name, from Hebrew, literally "watchful," from stem of 'ur "to awake, to rouse oneself."
Iran: from Persian Iran, from Middle Persian Ērān "(land) of the Iranians," genitive plural of ēr- "an Iranian," from Old Iranian *arya- (Old Persian ariya-, Avestan airya-) "Iranian", from Indo-Iranian *arya- or *ārya- (see Aryan), a self-designation, perhaps meaning "compatriot." In 1935 the government of Reza Shah Pahlavi requested governments with which it had diplomatic relations to call his country Iran, after the indigenous name, rather than the Greek-derived Persia.
Iranian: 1841 (adj.); 1873 (n.), from Iran + -ian.
Iraq: country name, 1920, from an Arabic name attested since 6c. for the region known in Greek as Mesopotamia; often said to be from Arabic `araqa, covering notions such as "perspiring, deeply rooted, well-watered," which may reflect the impression the lush river-land made on desert Arabs. But the name may be from, or influenced by, Sumerian Uruk (Biblical Erech), anciently a prominent city in what is now southern Iraq (from Sumerian uru "city").
irascibility (n.): 1750, from irascible + -ity.
irascible (adj.): late 14c., from Middle French irascible (12c.) and directly from Late Latin irascibilis, from Latin irasci "be angry, be in a rage," from ira "anger" (see ire).
irate (adj.): 1838, from Latin iratus "angry, enraged, violent, furious," past participle of irasci "grow angry," from ira "anger" (see ire).
ire (n.): c.1300, from Old French ire "anger, wrath, violence" (11c.), from Latin ira "anger, wrath, rage, passion," from PIE root *eis-, forming various words denoting "passion" cf. Greek hieros "filled with the divine, holy," oistros "gadfly," originally "thing causing madness;" Sanskrit esati "drives on," yasati "boils;" Avestan aesma "anger").

Old English irre in a similar sense is from an adjective irre "wandering, straying, angry," cognate with Old Saxon irri "angry," Old High German irri "wandering, deranged," also "angry;" Gothic airzeis "astray," and Latin errare "wander, go astray, angry" (see err (v.)).
Ireland: 12c., Anglo-Norman, with land + native Eriu (see Irish).
Irene: fem. proper name, from French Irène, from Latin Irene, from Greek Eirene, literally "peace, time of peace."
irenic: 1864; see eirenic.
irenology: "study of peace," 1974, from Greek eirene "peace" + -ology. Related: Irenological.
Irgun: militant Zionist organization, 1946, from Modern Hebrew, literally "organization," in full Irgun Zvai Leumi "national military organization."
iridescence: 1804, from iridescent + -ence. Related: Iridescency (1799).
iridescent: 1796, literally "rainbow-colored," coined from comb. form of Latin iris (genitive iridis) "rainbow" (see iris). Related: Iridescently.
iridium: 1804, Modern Latin, coined by its discoverer, English chemist Smithson Tennant (1761-1815) from Greek iris (genitive iridos) "rainbow;" so called for "the striking variety of colours which it gives while dissolving in marine acid" [Tennant]
iris (n.): late 14c., flowering plant (Iris germanica), also "prismatic rock crystal," from Latin iris (plural irides) "iris of the eye, iris plant, rainbow," from Greek iris (genitive iridos) "a rainbow; the lily; iris of the eye," originally "messenger of the gods," personified as the rainbow. The eye region was so called (early 15c. in English) for being the colored part; the Greek word was used of any brightly colored circle, "as that round the eyes of a peacock's tail" [Liddell and Scott].
Irish: c.1200, Irisce, from stem of Old English Iras "inhabitant of Ireland," from Old Norse irar, ultimately from Old Irish Eriu (accusative Eirinn, Erinn) "Erin," which is from Old Celtic *Iveriu (accusative *Iverionem, ablative *Iverione), perhaps from PIE *pi-wer- "fertile," literally "fat," from root *peie- "to be fat, swell" (see fat (adj.)).

Meaning "temper, passion" is 1834, American English (first attested in writings of Davy Crockett), from the legendary pugnacity of Irish people. Irish-American is from 1832; Irish coffee is from 1950. Wild Irish (late 14c.) originally were those not under English rule; Black Irish in reference to those of Mediterranean appearance is from 1888.
Irishman: c.1200, from Irish + man (n.).
irk (v.): mid-15c., irken "be weary of, be disgusted with;" earlier intransitive, "to feel weary" (early 14c.). Of uncertain origin, perhaps related to Old Norse yrkja "work" (from PIE root *werg- "to work;" see urge (v.)), or Middle High German erken "to disgust." Modern sense of "annoy" is from late 15c. An adjective, irk "weary, tired" is attested from c.1300 in northern and midlands writing.
irksome: "bothersome, burdensome," early 15c., from irk + -some. Related: Irksomely; irksomeness.
Irma: fem. proper name; see Emma.
iron (n.): Old English isærn (with Middle English rhotacism of -s-) "the metal iron; an iron weapon," from Proto-Germanic *isarnan (cf. Old Saxon isarn, Old Norse isarn, Middle Dutch iser, Old High German isarn, German Eisen) "holy metal" or "strong metal" (in contrast to softer bronze) probably an early borrowing of Celt. *isarnon (cf. Old Irish iarn, Welsh haiarn), from PIE *is-(e)ro- "powerful, holy," from PIE *eis "strong" (cf. Sanskrit isirah "vigorous, strong," Greek ieros "strong").
Right so as whil that Iren is hoot men sholden smyte. [Chaucer, c.1386]
Chemical symbol Fe is from the Latin word for the metal, ferrum (see ferro-). Meaning "metal device used to press or smooth clothes" is from 1610s. The adjective is Old English iren, isern. To have (too) many irons in the fire "to be doing too much at once" is from 1540s. Iron lung "artificial respiration tank" is from 1932.
iron (v.): c.1400, irenen, "to make of iron," from iron (n.). Meaning "press clothes" (with a heated flat-iron) is recorded from 1670s. Related: Ironed; ironing.
Iron Age: 1590s, originally from Greek and Roman mythology, the last and worst age of the world; the archaeological sense of "period in which humans used iron tools and weapons" is from 1879.
Iron Cross: from German das eiserne kreuz, instituted by Frederick Wilhelm III of Prussia, originally for distinguished military service in the wars against Napoleon.
Iron Curtain (n.): in reference to the Soviet occupation of Eastern Europe, famously coined by Winston Churchill March 5, 1946, in speech at Westminster College, Fulton, Missouri, but it had been used earlier in this context (e.g. by U.S. bureaucrat Allen W. Dulles at a meeting of the Council on Foreign Relations, Dec. 3, 1945). The figurative sense of "impenetrable barrier" is attested from 1819, and the specific sense of "barrier at the edge of the sphere of influence of the Soviet Union" is recorded from 1920. During World War II, Goebbels used it in German (ein eiserner Vorhang) in the same sense. Its popular use in the U.S. dates from Churchill's speech.
iron-gray: Old English isengrægum; see iron (n.) + gray. The color of freshly broken cast iron.
iron-on (adj.): 1959, from iron (v.) + on.
ironclad (adj.): 1852, of warships, American English, from iron (n.) + clad. Of contracts, etc., 1884. As a noun meaning "iron-clad ship," it is attested from 1862.
ironic: 1620s, from Late Latin ironicus, from Greek eironikos "dissembling, putting on a feigned ignorance," from eironeia (see irony). Related: Ironical (1570s); ironically.
ironing (n.): "act of pressing and smoothing clothes with a heated flat-iron," c.1710, from present participle of iron (v.). Ironing board attested from 1843.
Ironside: name given to a man of great hardihood or bravery, c.1300, first applied to Edmund II, king of England (d.1016), later also to Oliver Cromwell and his troops. Old Ironsides as a nickname of U.S.S. "Constitution" dates from that ship's defeat of H.M.S. "Guerriere" on Aug. 19, 1812, in the War of 1812.
ironwork (n.): early 15c., from iron (n.) + work (n.).