isotherm (n.) Look up isotherm at Dictionary.com
1860, from French isotherme (Humboldt, 1817), from Greek iso- (see iso-) + therme "heat" (see thermal).
isothermal Look up isothermal at Dictionary.com
1826 (adj.); 1852 (n.), from French isotherme (see isotherm) + -al (1).
isotonic (adj.) Look up isotonic at Dictionary.com
1828, from Greek isotonos "of level pitch; equally stretched," from iso- (see iso-) + tonos (see tenet).
isotope (n.) Look up isotope at Dictionary.com
1913, literally "having the same place," introduced by British chemist Frederick Soddy (1877-1956) on suggestion of Margaret Todd, from Greek isos "equal" (see iso-) + topos "place" (see topos); so called because despite the different atomic weights, the various forms of an element occupy the same place on the periodic table.
isotropic (adj.) Look up isotropic at Dictionary.com
1864, from iso- + Greek tropikos "belonging to a turning," from tropos "a turning, way, manner" (see trope).
Israel Look up Israel at Dictionary.com
Old English, "the Jewish people," from Latin Israel, from Greek, from Hebrew yisra'el "he that striveth with God" (Gen. xxxii.28), symbolic proper name conferred on Jacob and extended to his descendants, from sara "he fought, contended" + El "God." As an independent Jewish state in the country formerly called Palestine, it is attested from 1948.
Israeli Look up Israeli at Dictionary.com
1948; from Israel + Hebrew national designation suffix -i. Coined to distinguish citizens of the modern state from the ancient people who had been known in English since late 14c. as Israelites.
Israelite (n.) Look up Israelite at Dictionary.com
late 14c., from Latin israelita, from Greek Israelites, from Israel (see Israel).
Issachar Look up Issachar at Dictionary.com
son of Jacob by Leah (Old Testament), name of a biblical tribe of Israel, from Greek issakhar, from Hebrew Yissakhar, probably [Klein] from yesh sakhar "there is a reward" (see Gen. xxx:18).
Issei Look up Issei at Dictionary.com
c.1930s, term used among Japanese immigrants for first-generation immigrants, in Japanese, literally "first generation," related to ichi "one."
issuance (n.) Look up issuance at Dictionary.com
1863, American English, from issue (v.) + -ance.
issue (n.) Look up issue at Dictionary.com
c.1300, "exit, a going out, flowing out," from Old French issue "a way out, exit," from fem. past participle of issir "to go out," from Latin exire (source also of Italian uscire, Catalan exir), from ex- "out" (see ex-) + ire "to go," from PIE root *ei- "to go" (see ion). Meaning "discharge of blood or other fluid from the body" is from 1520s; sense of "offspring" is from late 14c. Meaning "outcome of an action" is attested from late 14c., probably from French; legal sense of "point in question at the conclusion of the presentation by both parties in a suit" (early 14c. in Anglo-French) led to transferred sense of "a point to be decided" (1836). Meaning "action of sending into publication or circulation" is from 1833.
issue (v.) Look up issue at Dictionary.com
c.1300, "to flow out," from issue (n.) or else from Old French issu, past participle of issir; sense of "to send out authoritatively" is from c.1600; that of "to supply (someone with something)" is from 1925. Related: Issued; issuing.
Istanbul Look up Istanbul at Dictionary.com
Turkish name of Constantinople, a corruption of Greek phrase eis tan (ten) polin "into the city," which is how the local Greek population referred to it. Picked up in Turkish 16c., though Turkish folk etymology traces the name to Islam bol "plenty of Islam." Greek polis "city" has been adopted into Turkish as a place-name suffix as -bolu.
isthmian (adj.) Look up isthmian at Dictionary.com
c.1600, from Latin isthmius, from Greek isthmios, from isthmos (see isthmus).
isthmus (n.) Look up isthmus at Dictionary.com
1550s, from Latin isthmus, from Greek isthmos "narrow passage, narrow neck of land," especially that of Corinth, of unknown origin, perhaps from eimi "to go" + suffix -thmo (compare ithma "a step, movement").
it (pron.) Look up it at Dictionary.com
Old English hit, neuter nominative and accusative of third person singular pronoun, from Proto-Germanic demonstrative base *khi- (cognates: Old Frisian hit, Dutch het, Gothic hita "it"), from PIE *ko- "this" (see he). Used in place of any neuter noun, hence, as gender faded in Middle English, it took on the meaning "thing or animal spoken about before."
Whether the charmer sinner it or saint it,
If the folly grow romantic, I must paint it.
[Pope, "Moral Essays," 1735]
The h- was lost due to being in an unemphasized position, as in modern speech the h- in "give it to him," "ask her," "is only heard in the careful speech of the partially educated" [Weekley]. It "the sex act" is from 1610s; meaning "sex appeal (especially in a woman)" first attested 1904 in works of Rudyard Kipling, popularized 1927 as title of a book by Elinor Glyn, and by application of It Girl to silent-film star Clara Bow (1905-1965). In children's games, meaning "the one who must tag the others" is attested from 1842.
Italian (n.) Look up Italian at Dictionary.com
early 15c., "native of Italy," from Italian Italiano, from Italia "Italy" (see Italy). As an adjective from 1640s.
Italianate (adj.) Look up Italianate at Dictionary.com
1570s, from Italian Italianato "rendered Italian," from Italiano (see Italian).
italic Look up italic at Dictionary.com
1610s (adj.), 1670s (n.) "italic type," from Latin italicus "Italian" (see Italian); so called because it was introduced in 1501 by Aldus Manutius, printer of Venice (who also gave his name to Aldine), and first used in an edition of Virgil dedicated to Italy. Earlier (1570s) the word was used for the plain, sloping style of handwriting, as opposed to Gothic. Related: Italics.
italicize (v.) Look up italicize at Dictionary.com
"to print in italics" (for emphasis, etc.), 1795, from italic + -ize. Related: Italicized; italicizing.
Italy Look up Italy at Dictionary.com
from Latin Italia, from Greek Italia, perhaps from an alteration of Oscan Viteliu "Italy," but originally only the southwestern point of the peninsula, traditionally from Vitali, name of a tribe that settled in Calabria, whose name is perhaps somehow connected with Latin vitulus "calf," or perhaps the country name is directly from vitulus as "land of cattle," or it might be from an Illyrian word, or an ancient or legendary ruler Italus.
itch (n.) Look up itch at Dictionary.com
Old English gicce, from giccan (v.) "to itch" (see itch (v.)). Sense of "restless desire" is first attested 1530s; itching in this sense is from mid-14c.
itch (v.) Look up itch at Dictionary.com
Old English giccan "to itch," from West Germanic *jukkjan (cognates: Middle Dutch jöken "to itch," Old High German jucchen, German jucken). Related: Itched; itching.
itchy (adj.) Look up itchy at Dictionary.com
Old English giccig; see itch + -y (2). Figurative itchy palm is attested by 1590s. Related: Itchiness.
item Look up item at Dictionary.com
late 14c. (adv.) "moreover, in addition," from Latin item (adv.) "likewise, just so, moreover," used to introduce a new fact or statement, probably from ita "thus," id "it" (see id) + adverbial ending -tem (compare idem "the same"). Thus "a statement or maxim" (of the kind formerly introduced by the word item), first recorded 1560s. Meaning "detail of information" (especially in a newspaper) is from 1819; item "sexually linked unmarried couple" is 1970, probably from notion of being an item in the gossip columns. Noun sense of "an article of any kind" (1570s) developed from adverbial sense of "moreover, in addition," which was used before every article in a list (such as an inventory or bill).
itemize (v.) Look up itemize at Dictionary.com
1864, American English, from item + -ize. Related: Itemized; itemizing. Earlier verb was simply item (c.1600).
iterate (v.) Look up iterate at Dictionary.com
1530s, "to do again, repeat," back-formation from iteration, or else from Latin iteratus, past participle of iterare. Related: Iterated; iterating.
iteration (n.) Look up iteration at Dictionary.com
late 15c., from Latin iterationem (nominative iteratio) "repetition," noun of action from past participle stem of iterare "do again, repeat," from iterum "again," from PIE *i-tero-, from pronomial root *i- (see yon).
iterative (adj.) Look up iterative at Dictionary.com
"involving repetition," late 15c., from French iteratif (c.1400), from Late Latin iterativus, from iterat-, past participle stem of iterare (see iteration). As a noun, from 1854. Related: Iteratively.
Ithaca Look up Ithaca at Dictionary.com
western Greek Island, legendary home of Odysseus; the first element is perhaps Phoenician I "island;" the rest is unknown.
ither Look up ither at Dictionary.com
Scottish form of other.
ithyphallic Look up ithyphallic at Dictionary.com
1610s, "poem in ithyphallic meter," from Greek ithyphallos "phallos carried in the festivals," from ithys "straight" + phallos "erect penis" (see phallus). As an adjective from 1795. The meter was that of the Bacchic hymns, which were sung in the rites during which such phalloses were carried. Thus, in Victorian times, the word also meant "grossly indecent" (1864).
itinerant (adj.) Look up itinerant at Dictionary.com
1560s (attested in Anglo-Latin from late 13c.), from Late Latin itinerantem (nominative itinerans), present participle of itinerare "to travel," from Latin iter (genitive itineris) "journey," from ire "go" (see ion). Originally in reference to circuit courts.
itinerary (n.) Look up itinerary at Dictionary.com
mid-15c., "route of travel," from Late Latin itinerarium "account of a journey," noun use of neuter of itinerarius "of a journey," from Latin itineris "journey" (see itinerant). By late 15c. it meant "record of a journey;" extended sense "sketch of a proposed route" is from 1856.
itinerate (v.) Look up itinerate at Dictionary.com
c.1600, from Late Latin itineratus, past participle of itinerare "to travel" (see itinerant). Especially "to travel from place to place preaching" (1775). Related: Itinerated; itinerating.
its Look up its at Dictionary.com
neuter possessive pronoun; the modern word begins to appear in writing at the end of 16c., from it + genitive/possessive ending 's (q.v.), and "at first commonly written it's, a spelling retained by some to the beginning of the 19c." [OED]. The apostrophe came to be omitted, perhaps because it's already was established as a contraction of it is, or by general habit of omitting apostrophes in personal pronouns (hers, yours, theirs, etc.).

The neuter genitive pronoun in Middle English was his, but the clash between grammatical gender and sexual gender, or else the application of the word to both human and non-human subjects, evidently made users uncomfortable. Restriction of his to the masculine and avoidance of it as a neuter pronoun is evidenced in Middle English, and of it and thereof (as in KJV) were used for the neuter possessive. Also, from c.1300, simple it was used as a neuter possessive pronoun. But in literary use, his as a neuter pronoun continued into the 17c.
itself (pron.) Look up itself at Dictionary.com
late 14c., from Old English hit sylf, from it + self. Since 17c. usually regarded as its self (compare its own self).
itsy-bitsy (adj.) Look up itsy-bitsy at Dictionary.com
"charmingly small," 1890, from itty and/or bitsy. Bitsy-itsy is recorded from 1875.
itty (adj.) Look up itty at Dictionary.com
1798, in a letter of Jane Austen, baby-talk form of little. Related: itty-bitty (1855); tiddy-itty (1852).
Ivan Look up Ivan at Dictionary.com
masc. proper name, from Russian, literally "John," from Greek Ioannes "John." As the personification of Russia, or the typical name for a Russian man (originally a Russian soldier), attested from 1870.
ivory (n.) Look up ivory at Dictionary.com
mid-13c. (late 12c. as a surname), Anglo-French ivorie, from Old North French ivurie (12c.), from Latin eboreus "of ivory," from ebur (genitive eboris) "ivory," probably via Phoenician from an African source (compare Egyptian ab "elephant," Coptic ebu "ivory"). Replaced Old English elpendban, literally "elephant bone." Applied in slang to articles made from it, such as dice (1830) and piano keys (1854). As a color, especially in reference to human skin, it is attested from 1580s. Ivories as slang for "teeth" dates from 1782. Related: Ivoried.
ivory tower (n.) Look up ivory tower at Dictionary.com
as a symbol of artistic or intellectual aloofness, by 1889, from French tour d'ivoire, used in 1837 by critic Charles-Augustin Sainte-Beuve (1804-1869) with reference to the poet Alfred de Vigny, whom he accused of excessive aloofness.
Et Vigny, plus secret, comme en sa tour d'ivoire, avant midi rentrait. [Sainte-Beuve, "Pensées d'Août, à M. Villemain," 1837]
Used earlier as a type of a wonder or a symbol of "the ideal." The literal image is perhaps from Song of Solomon [vii:4]:
Thy neck is as a tower of ivory; thine eyes like the fishpools in Heshbon, by the gate of Bathrabbim: thy nose is as the tower of Lebanon which looketh toward Damascus. [KJV]
ivy (n.) Look up ivy at Dictionary.com
Old English ifig, from West Germanic *ibakhs (cognates: Middle Low German iflof, Dutch eiloof, Old High German ebahewi, German Efeu), of unknown origin; the second element in the Old High German word might be "hay."

Ivy bush as a sign of a tavern where wine is served is attested from mid-15c. Ivy League, inspired by the notion of old, ivy-coated walls, dates to 1933 (perhaps originally in reference to football; it consists of Brown, Columbia, Cornell, Dartmouth, Harvard, Pennsylvania, Princeton, and Yale).
ixnay Look up ixnay at Dictionary.com
"no, no more," pig Latin for nix.
izard (n.) Look up izard at Dictionary.com
chamois-like antelope of the Pyrenees, 1791, from French isard, Gascon isart, "perhaps of Iberian origin," or [Klein] from Basque (which has izzara "star").
izzard (n.) Look up izzard at Dictionary.com
old name for "Z," 1738, a variant of zed.