Online Etymology Dictionary

invitational (adj.): 1894, from invitation + -al (1). The noun is by 1940, short for invitational tournament.
invitatory (adj.): 1640s, from Latin invitatorius "inviting," from invitat-, past participle stem of invitare "to invite, treat, entertain" (see invitation).
invite (v.): "solicit to come," 1530s, a back-formation from invitation, or else from Middle French inviter (15c.), from Latin invitare "to invite," also "to summon, challenge; to feast, to entertain," a word of uncertain origin. Related: Invited; inviting.
invite (n.): "an invitation," 1650s, from invite (v.).
invitee (n.): 1837, from invite (v.) + -ee.
inviting (adj.): "attractive, alluring," c. 1600, present-participle adjective from invite (v.). Related: Invitingly.
invocation (n.): late 14c., "petition (to God or a god) for aid or comfort; invocation, prayer;" also "a summoning of evil spirits," from Old French invocacion "appeal, invocation" (12c.), from Latin invocationem (nominative invocatio), noun of action from past participle stem of invocare "to call upon, invoke, appeal to" (see invoke).
invoice (n.): "written account of the particulars and prices of merchandise shipped or sent," 1550s, apparently from Middle French envois, plural of envoi "dispatch (of goods)," literally "a sending," from envoyer "to send" (see envoy). As a verb, 1690s, from the noun.
invoke (v.): late 15c., from Old French invoquer, envoquer, envochier "invoke, implore" (12c.), from Latin invocare "call upon, implore," from in- "upon" (see in- (2)) + vocare "to call," related to noun vox (genitive vocis) "voice" (see voice (n.)). Related: Invoked; invoking.
involuntary (adj.): mid-15c., from Late Latin involuntarius "involuntary, unwilling," from in- "not, opposite of" (see in- (1)) + Latin voluntarius "willing, voluntarily" (see voluntary). Related: Involuntarily.
involute (adj.): early 15c., "wrapped," from Latin involutus "rolled up, intricate, obscure," past participle of involvere "envelop, surround; roll into, wrap up" (see involve).
involution (n.): late 14c., "condition of being twisted or coiled; a fold or entanglement," originally in anatomy, from Late Latin involutionem (nominative involutio) "a rolling up," noun of action from past participle stem of Latin involvere "envelop, surround, roll into" (see involve). Related: Involutional.
involve (v.): late 14c., "envelop, surround; make cloudy or obscure," from Old French involver and directly from Latin involvere "envelop, surround, overwhelm," literally "roll into," from in- "in" (see in- (2)) + volvere "to roll" (see volvox). Mid-15c. as "concern oneself." Sense of "take in, include" first recorded c. 1600. Related: Involved; Involving.
Obscurest night involved the sky,
The Atlantic billows roared,

[Cowper, "The Castaway"]
involved (adj.): "complicated," 1640s, past participle adjective from involve. Earlier it meant "spirally curved" (1610s).
involvement (n.): 1706, from involve + -ment.
invulnerability (n.): 1707, from invulnerable + -ity.
invulnerable (adj.): 1590s, from Latin invulnerabilis "invulnerable," from in- "not" (see in- (1)) + vulnerabilis (see vulnerable). Related: Invulnerably.
inward (adj.): Old English inweard "inmost; sincere; internal, intrinsic; deep," from Proto-Germanic *inwarth "inward" (source also of Old Norse innanverðr, Old High German inwart, Middle Dutch inwaert), from root of Old English inne "in" (see in (adv.)) + -weard (see -ward). As an adverb, Old English inneweard. As a noun in late Old English, "entrails, intestines."
inwardly (adv.): Old English inweardlice; see inward + -ly (2).
inwardness (n.): late 14c., from inward + -ness.
inwit (n.): Middle English word formed to translate Latin conscientia; early 13c., "conscience;" c. 1300, "reason, intellect," from in (adj.) + wit (n.). Not related to Old English inwit, which meant "deceit." Joyce's use of it in "Ulysses" (1922) echoes the title of the 14c. work "Ayenbite of Inwyt" ("Remorse of Conscience," a translation from French), is perhaps the best-known example of the modern use of the word as a conscious archaism, but not the earliest.
Þese ben also þy fyve inwyttys: Wyl, Resoun, Mynd, Ymaginacioun, and Thoght [Wyclif, c. 1380]

If ... such good old English words as inwit and wanhope should be rehabilitated (and they have been pushing up their heads for thirty years), we should gain a great deal. [Robert Bridges, English poet laureate, 1922]
inwork (v.): 1680s, from in (adv.) + work (v.).
Io: in Greek mythology, daughter of the river god Inachus, she was pursued by Zeus, who changed her to a heifer in a bid to escape the notice of Juno, but she was tormented by a gadfly sent by Juno. The Jovian moon was discovered in 1610 and named for her by Galileo.
iodic (adj.): 1815, from French iodic (1812); see iodine + -ic.
iodide (n.): compound of iodine, 1822, from iod-, comb. form of iodine used before vowels + -ide.
iodine (n.): non-metallic element, 1814, formed by English chemist Sir Humphrey Davy (1778-1829) from French iode "iodine," which was coined 1812 by French chemist Joseph Louis Gay-Lussac from Greek ioeides "violet-colored" (from ion "the violet; dark blue flower;" see violet) + eidos "appearance" (see -oid).

Davy added the chemical suffix -ine (2) to make it analogous with chlorine and fluorine. So called from the color of the vapor given off when the crystals are heated.
iodize (v.): "add iodine to, treat with iodine," 1841, from 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- (1) "to go, to walk." So called because ions move toward the electrode of opposite charge.

The root is an enormously productive one, the source also of 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."
Ionian (adj.): 1590s, "of Ionia," the districts of ancient Greece inhabited by the Ionians, one of the three (or four) great divisions of the ancient Greek people. 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. As a noun from 1560s.

Ionia included Attica, Euboea, and the north coast of the Peloponnesus, but it especially referred to the coastal strip of Asia Minor, including the islands of Samos and Chios. The old Ionic dialect was the language of Homer and Herodotus, and, via its later form, Attic, that of all the great works of the Greeks. The name also was given to the sea that lies between Sicily and Greece, and the islands in it (1630s in English in this sense). The musical Ionian mode (1844) corresponds to our C-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 (adj.): "pertaining to ions," 1890, from ion + -ic.
Ionic (adj.): "pertaining to Ionia or the Ionians," 1570s of music; 1580s of architecture, from Latin Ionicus, from Greek Ionikos (see Ionian). In prosody, a foot of two long syllables followed by two short. The Ionic school of philosophers (Thales, Anaxamander, etc.) studied the material world in ways that somewhat anticipated observational science. It also once was the name of an important school of Greek painting, but all of it save the name is lost. Related: Ionicize (1841).
ionization (n.): 1891; see ionize + -ation.
ionize (v.): 1896, from ion + -ize. Related: Ionized; ionizing. Unrelated to Ionize "to make Ionic in form or fact" (1816), for which see Ionian.
ionosphere (n.): region of the outer atmosphere, 1926, from ion + sphere. Coined by Scottish radar pioneer Robert A. Watson-Watt (1892-1973). So called because it contains many ions.
iopterous (adj.): "having violet wings," 1855, from Greek ion "violet, violet color" (see iodine) + pteron "wing" (see ptero-).
iota (n.): "very small amount," 1630s, figurative use of iota, ninth and smallest letter in the Greek alphabet (corresponding to Latin -i-). Its use in this sense is after Matt. v:18 (see jot (n.), which is the earlier form of the name in English), but iota in classical Greek also was proverbially used of anything very small. The letter name is from Semitic (compare Phoenician and Hebrew yodh).
IOU: also I.O.U., I O U, 1610s, originally written IOV (see V); a punning on "I Owe You." "A memorandum or acknowledgement of debt less formal than a promissory note, because no direct promise to pay is expressed." [Century Dictionary]
Iowa: organized as a U.S. territory 1838; admitted as a state 1846, named for the river, ultimately from the name of the native people, of the Chiwere branch of the Aiouan family; said to be from Dakota ayuxba "sleepy ones," or from an Algonquian language (Bright cites Miami/Illinois /aayohoowia/). On a French map of 1673 it appears as Ouaouiatonon. Related: Iowan.
IPA (n.): also I.P.A., 1952, abbreviation of India pale ale.
ipecac (n.): dried root of a South American shrub, used as an emetic, purgative, nauseant, etc., 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. Hence, "an assertion made without proof, resting entirely on the authority of the speaker" (1590s), ipsedixitism "practice of dogmatic assertion" (1830, Bentham), etc.
ipseity (n.): "personal identity, individuality, selfhood," 1650s, from Latin ipse "self" + -ity.
ipsilateral (adj.): "on the same side of the body," 1907, from Latin ipse "self" + lateral (adj.). Related: Ipsilaterally.
ipso facto: Latin adverbial phrase, literally "by that very fact, by the fact itself," from neuter ablative of ipse "he, himself, self" + ablative of factum "fact" (see fact).
ir-: assimilated form of the two Latin prefixes in- "not," or "in" (see in-) before -r-.
Ira: masc. proper name, from Hebrew, literally "watchful," from stem of 'ur "to awake, to rouse oneself."
iracund (adj.): "angry, inclined to wrath," 1707, from Late Latin iracundus, from ira "anger, wrath, rage, passion" (see ire (n.)). Related: Iracundulous (1765).
[T]he Severn is so mischievous and cholerick a river, and so often ruins the country with sudden inundations, since it rises in Wales, and consequently participates sometimes of the nature of that hasty, iracund people among whom 'tis born. [Thomas Browne, "Letters from the Dead to the Living," 1707]
Iran: country name, 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-, a self-designation, perhaps meaning "compatriot" (see Aryan).

In English it began to be used 1760s, by orientalists and linguists (Alexander Dow, William Jones), in historical contexts, and usually with a footnote identifying it with modern Persia; as recently as 1903 "Century Dictionary" defined it as "the ancient name of the region lying between Kurdistan and India." 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 (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.
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 desert Arabs' impression of the lush river-land. But the name might be from, or influenced by, Sumerian Uruk (Biblical Erech), anciently a prominent city in what is now southern Iraq (from Sumerian uru "city"). Related: Iraqi (attested in English from 1777, in reference to regional Mesopotamian music or dialects).