Online Etymology Dictionary

inveterate (adj.): late 14c., "old," from Latin inveteratus "of long standing, chronic, old," past participle of inveterare "become old in," from in- "in, into" (see in- (2)) + verb from vetus (genitive veteris) "old" (see veteran). From early 15c. as "firmly established by long continuance;" from c. 1500, of persons, "hardened, confirmed" (in habit, etc.). Related: Inveterateness.
invidious (adj.): c. 1600, from Latin invidiosus "full of envy, envious" (also "exciting hatred, hateful"), from invidia "envy, grudge, jealousy, ill will" (see envy (n.)). Envious is the same word, but passed through French. Related: Invidiously; invidiousness.
invigorate (v.): 1640s, from in- (2) + vigor (n.) + -ate (2). Earlier verb was envigor (1610s), from Old French envigorer. Related: Invigorated; invigorating.
invincible (adj.): early 15c., from Old French invincible (14c.) or directly from Latin invincibilis "unconquerable," from in- "not" (see in- (1)) + vincibilis "to be gained, easily maintained, conquerable," from vincere "to overcome" (see victor). Related: Invincibly.

The noun meaning "one who is invincible" is from 1630s. Invincible ignorance, an ignorance which the person having it lacks means to overcome, is from Church Latin ignorantia invincibilis (Aquinas). The Invincible Armada was the Spanish of 1588. Related: Invincibly.
inviolable (adj.): mid-15c., "that is to be kept without violation" (of an oath, etc.), from Latin inviolabilis "inviolable, invulnerable," from in- "not, opposite of" (see in- (1)) + violabilis "that may be injured, easily wounded," from violare "to do violence to" (see violation). Meaning "having a right or guaranty of immunity" (of a place of sanctuary, etc.) is from 1570s. Meaning "incapable of being injured" is from 1520s. Related: Inviolably.
invisible (adj.): mid-14c., "not perceptible to sight, incapable of being seen," from Old French invisible (13c.), from Latin invisibilis "unseen, not visible," from in- "not" (see in- (1)) + visibilis (see visible). Meaning "kept out of sight" is from 1640s. As a noun, "things invisible," from 1640s. Invisible Man is from H.G. Wells's novel (1897); invisible ink is from 1680s. Related: Invisibly.
invitation (n.): mid-15c., "act of inviting, solicitation," from Latin invitationem (nominative invitatio) "an invitation, incitement, challenge," noun of action from past participle stem of invitare "invite, treat, entertain," originally "be pleasant toward," from in- "toward" (see in- (2)).

The second element is obscure. Watkins suggests a suffixed form of the PIE root *weie- "to go after something, pursue with vigor" (see gain (v.)); de Vaan also traces it to a PIE form meaning "pursued." Meaning "the spoken or written form in which a person is invited" is from 1610s.
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.
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"]
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."
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]
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.
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]
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.
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).
I.Q.: 1922, abbreviation of intelligence quotient, a 1921 translation of German Intelligenz-quotient, coined 1912 by German psychologist William L. Stern (1871-1938).
Intelligence is a general capacity of an individual consciously to adjust his thinking to new requirements: it is general mental adaptability to new problems and conditions of life. [Stern, "The Psychological Methods of Testing Intelligence," 1914]
Earlier, i.q. was an abbreviation of Latin idem quod "the same as."
Ira: masc. proper name, from Hebrew, literally "watchful," from stem of 'ur "to awake, to rouse oneself."
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.
irascible (adj.): late 14c., from Old French irascible (12c.) and directly from Late Latin irascibilis, from Latin irasci "be angry, be in a rage," from ira "anger" (see ire).
Irascible indicates quicker and more intense bursts of anger than irritable, and less powerful, lasting, or manifest bursts than passionate. [Century Dictionary]
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- (1), forming various words denoting passion (source also of Greek hieros "filled with the divine, holy," oistros "gadfly," originally "thing causing madness;" Sanskrit esati "drives on," yasati "boils;" Avestan aesma "anger;" Lithuanian aistra "violent passion").

Old English irre in a similar sense is unrelated; it from an adjective irre "wandering, straying, angry," which is 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.)).
Irene: fem. proper name, from French Irène, from Latin Irene, from Greek Eirene, literally "peace, time of peace."
irenic (adj.): "promoting peace," 1854, from Greek eirenikos, from eirene "peace, time of peace." Earlier as irenical (1650s). Irenics is from 1834, originally a branch of theology.
Irgun: militant Zionist organization, 1946, from Modern Hebrew, literally "organization," in full Irgun Zvai Leumi "national military organization."
iridescent (adj.): 1784, literally "rainbow-colored," coined from Latin iris (genitive iridis) "rainbow" (see iris). The verb iridesce (1868) is a back-formation. Related: Iridescently.
iridium (n.): silver-white metallic element, 1804, coined in Modern Latin by its discoverer, English chemist Smithson Tennant (1761-1815) from Greek iris (genitive iridos) "rainbow" (see iris) + chemical ending -ium. So called "from the striking variety of colours which it gives while dissolving in marine acid" [Tennant]
iris (n.): late 14c. as the name of a flowering plant (Iris germanica); early 15c. in reference to the eye membrane, from Latin iris (plural irides) "iris of the eye; iris plant; rainbow," from Greek iris (genitive iridos) "a rainbow;" also "iris plant" and "iris of the eye," a word of uncertain origin. Iris was the name of the minister and messenger of the Olympian gods (especially of Hera), visibly represented by the rainbow (which was regarded as the descent of a celestial messenger). From the oldest parts of the Iliad the word is used of both the messenger and the rainbow.

The eye region was so called (early 15c. in English) for being the part that gives color to the eye; the Greek word was used of any brightly colored circle, "as that round the eyes of a peacock's tail" [Liddell & Scott]. Another sense in Middle English was "prismatic rock crystal." Related: Iridian; iridine.
Irish (n.): c. 1200, "the Irish people," from Old English Iras "inhabitant of Ireland." This is from Old Norse irar, which comes ultimately from Old Irish Eriu (accusative Eirinn, Erinn) "Erin." The reconstructed ancestry of this derives it from Old Celtic *Iveriu (accusative *Iverionem, ablative *Iverione), perhaps (Watkins) from PIE *pi-wer- "fertile," literally "fat," from root *peie- "to be fat, swell" (see fat (adj.)).

From mid-15c. in reference to the Celtic language spoken in Ireland. Some Middle English forms of the word suggest influence of (or punning on) Old French irais, irois "wrathful, bad-tempered" (literally "ire-ous") and Irais "Irish."

Meaning "temper, passion" is 1834, American English (first attested in writings of Davy Crockett), from the legendary pugnacity of the Irish. Irish-American (n.) is from 1816 (as an adjective from 1820). Wild Irish (late 14c.) originally were those not under English rule; Black Irish in reference to those of Mediterranean appearance is from 1888.
irk (v.): early 15c., irken, "to trouble (someone), disturb, hinder, annoy;" earlier "be lax, slow, or unwilling (in doing something); be displeased or discontented" (early 14c.); "be weary of, be disgusted with" (c. 1400); of uncertain origin.

Watkins suggests it is related to Old Norse yrkja "work." Middle High German erken "to disgust" also has been suggested. A Middle English adjective, irk, meaning "weary, tired, bored; distressed, troubled; troublesome, annoying," is attested from c. 1300 in Northern and Midlands writing; it is sometimes said to be from the verb, but it is older, and "Middle English Dictionary" says this is probably Celtic, and compares Old Irish arcoat "he injures," erchoat "harm, injury."
iron (n.): Middle English iron, iren, yron, from Old English iren, variant (with rhotacism of -s-) of isen, later form of isern, isærn "the metal iron; an iron weapon or instrument," from Proto-Germanic *isarnan (source also of Old Saxon isarn, Old Frisian isern, Old Norse isarn, Middle Dutch iser, Old High German isarn, German Eisen).

This probably is an early borrowing of Celtic *isarnon (compare Old Irish iarn, Welsh haiarn), which Watkins suggests is from PIE *is-(e)ro- "powerful, holy," from PIE *eis "strong" (source also of Sanskrit isirah "vigorous, strong," Greek ieros "strong"), on the notion of "holy metal" or "strong metal" (in contrast to softer bronze).

It was both an adjective and a noun in Old English, but in form it is an adjective. The alternative isen survived into early Middle English as izen. In southern England the Middle English word tended to be ire, yre, with loss of -n, perhaps regarded as an inflection; in the north and Scotland, however, the word tended to be contracted to irn, yrn, still detectable in dialect.
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. Meaning "golf club with an iron head, 1842. 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. The iron crown was that of the ancient kings of Lombardy, with a thin band of iron in the gold, said to have been forged from a nail of Christ's Cross. Iron horse "railroad locomotive" is from an 1839 poem. Iron maiden, instrument of torture, is from 1837 (probably translating German eiserne jungfrau). The unidentified French political prisoner known as the man in the iron mask died in the Bastille in 1703. In British history, Wellington was called the Iron Duke by 1832.
Iron Age: 1590s, originally, as in 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 1866 (earlier in this sense iron period, 1847).
ironclad (adj.): 1852 of knights, 1861, of warships, American English, from iron (n.) + clad. Figuratively, of contracts, etc., "very rigid or strict, allowing no evasion or escape," from 1884. As a noun meaning "iron-clad ship," it is attested from 1862.
Iron Cross: from German eiserne kreuz, instituted 1813 by Frederick Wilhelm III of Prussia, originally for distinguished military service in the wars against Napoleon.
iron curtain (n.): 1794, the name of a fire-protection device to be used in theaters, a literal iron curtain; see iron (n.) + curtain (n.).
The new and exquisitely beautiful theatre of Drury-lane has the peculiar contrivance of an iron-curtain to secure the audience from all danger, in case of fire on the stage. Miss Farren, in the occasional epilogue, delivered on opening this new theatre, pleasantly informs the spectators that, should flames burst out in the part appropriated to the representation, they may comfort themselves with thinking that nothing can be burnt but the scenery and the actors. ["The Monthly Review," June 1794]
From 1819 in the figurative sense "impenetrable barrier." 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 (for example by U.S. bureaucrat Allen W. Dulles at a meeting of the Council on Foreign Relations, Dec. 3, 1945). The phrase had been used in the sense of "barrier at the edge of the sphere of influence of the Soviet Union" from 1920. During World War II, Goebbels used it in German (ein eiserner Vorhang) in the same sense. But its popular use in the U.S. dates from Churchill's speech.
irony (n.): "figure of speech in which the intended meaning is the opposite of the literal meaning" (usually covert sarcasm under a serious or friendly pretense), c. 1500, from Latin ironia, from Greek eironeia "dissimulation, assumed ignorance," from eiron "dissembler," perhaps related to eirein "to speak," from PIE *wer-yo-, suffixed form of root *were- (3) "to speak" (see verb). Used in Greek of affected ignorance, especially that of Socrates, as a method of exposing an antagonist's ignorance by pretending to modestly seek information or instruction from him. Thus sometimes in English in the sense "simulated ignorance."

For nuances of usage, see humor (n.). In early use often ironia. Figurative use for "condition opposite to what might be expected; contradictory circumstances; apparent mockery of natural or expected consequences" is from 1640s, sometimes distinguished as irony of fate or irony of circumstances. Related: Ironist. A verb ironize "speak ironically" is recorded from c. 1600.
Iroquois: 1660s (adj.); 1670s (n.) "member of the confederated Indian tribes of central New York," from French (c. 1600); not an Iroquoian word, perhaps from an Algonquian language. Related: Iroquoian (1690s). Originally the Mohawks, Oneidas, Onodagas, Cayugas, and Senecas.
irradiate (v.): c. 1600, "to cast beams of light upon," from Latin irradiatus, past participle of irradiare "shine forth, beam upon, illumine," from assimilated form of in- "into, in" (see in- (2)) + radiare "to shine" (see radiate (v.)). Meaning "expose to radiation other than light" (originally X-rays) is from 1901. Related: Irradiated; irradiating.
irrational (adj.): late 15c., "not endowed with reason" (of beasts, etc.), from Latin irrationalis/inrationalis "without reason, not rational," from assimilated form of in- "not, opposite of" (see in- (1)) + rationalis "of or belonging to reason, reasonable" (see rational (adj.)).

Meaning "illogical, absurd" is attested from 1640s. Related: Irrationally. The mathematical sense "inexpressible in ordinary numbers" is from late 14c. in English, from use of the Latin word as a translation of Greek alogon in Euclid.
Irredentist (n.): 1882, member of Italian political party formed 1878 which demanded the annexation of neighboring regions where a part of the population was Italian-speaking (Trieste, South Tyrol, Nice, Corsica, etc.); from Italian Irredentista, from irredenta (Italia) "unredeemed (Italy)," fem. of irredento, from in- "not, opposite of" (see in- (1)) + redento, from Latin redemptus, past participle of redimere (see redemption). Related: Irredentism.
irrefragable (adj.): "that cannot be refuted," literally "incapable of being broken down," 1530s, from French irréfragable (16c.) and directly from Late Latin irrefragabilis, from assimilated form of in- "not, opposite of" (see in- (1)) + Latin refragari "to oppose, contest," from re- "back" (see re-) + frag-, base of frangere "to break" (see fraction). Related: irrefragably; irrefragability.
irrefrangible (adj.): 1722, "that cannot be broken or violated," from assimilated form of in- "not, opposite of" (see in- (1)) + refrangible. Related: Irrefrangibly.
irrefutable (adj.): "incapable of being disproved," 1610s, from Late Latin irrefutabilis "irrefutable," from assimilated form of in- "not, opposite of" (see in- (1)) + refutabilis "refutable," from refutare (see refute). Related: Irrefutably; irrefutability.
irregardless (adj.): an erroneous word that, etymologically, means the opposite of what it is used to express; probably a blend of irrespective and regardless, and perhaps inspired by the colloquial use of the double negative as an emphatic. Attested from at least 1870s (e.g. "Portsmouth Times," Portsmouth, Ohio, U.S.A., April 11, 1874: "We supported the six successful candidates for Council in the face of a strong opposition. We were led to do so because we believed every man of them would do his whole duty, irregardless of party, and the columns of this paper for one year has [sic] told what is needed.").
irregular (adj.): late 14c., "not in conformity with Church rules," from Old French irreguler "irregular, incapable, incompetent" (13c., Modern French irrégulier), from Medieval Latin irregularis "not regular," from assimilated form of in- "not, opposite of" (see in- (1)) + Latin regularis "having rules" (see regular (adj.)). General sense of "not conforming to regular rules or principles" is from late 15c. "It expresses the fact of being out of conformity with rule, but implies nothing more with certainty. Yet the word is sometimes used in a sinister sense, as though it were a euphemism for something worse." [Century Dictionary] Meaning "unsymmetrical" is from 1580s. In reference to variable stars, from 1797.
irreligious (adj.): c. 1400, from Late Latin irreligiosus "irreligious, impious," from assimilated form of in- "not, opposite of" (see in- (1)) + religiosus (see religious). Related: Irreligiously.