Online Etymology Dictionary

intestines (n.): "bowels," 1590s, from intestine, based on Latin intestina, neuter plural of intestinus (adj.) "internal, inward, intestine," from intus "within, on the inside," from PIE *entos, suffixed form of root *en "in" (see in (adv.)). Compare Sanskrit antastyam, Greek entosthia "bowels." The Old English word was hropp, literally "rope."
Intifada (n.): "Palestinian revolt," 1985, from Arabic, literally "a jumping up" (in reaction to something), from the verb intafada "to be shaken, shake oneself."
intimate (adj.): 1630s, "closely acquainted, very familiar," also "inmost, intrinsic," from Late Latin intimatus, past participle of intimare "make known, announce, impress," from Latin intimus "inmost, innermost, deepest" (adj.), also used figuratively, of affections, feelings, as a noun, "close friend;" superlative of in "in" (see in- (2)). Intimate (adj.) used euphemistically in reference to women's underwear from 1904. Related: Intimately.
intimate (v.): 1530s, "make known formally;" 1580s, "suggest indirectly," back-formation from intimation (which could explain the pronunciation) or else from Late Latin intimatus, past participle of intimare "to make known." The Old French verb was intimer. Related: Intimated; intimating.
intimidate (v.): 1640s, from Medieval Latin intimidatus, past participle of intimidare "to frighten, make afraid," from in- "in" (see in- (2)) + Latin timidus "fearful" (see timid). Related: Intimidated; intimidating. The French verb was intimider (16c.).
into (prep.): Old English into "into, to, against, in," originally in to. It emerged in late Old English to do the work of the dative case inflections, then fading, that formerly distinguished, for instance, the notion of "in the house" from that of "into the house." Compare onto, unto. To be into (something) "be intensely involved in or devoted to" recorded by 1967 in American English youth slang.
intolerable (adj.): late 14c., from Latin intolerabilis "that cannot bear; that cannot be borne," from in- "not, opposite of" (see in- (1)) + tolerabilis "that may be endured," from tolerare "to bear, endure" (see toleration). Related: Intolerably.
intone (v.1): late 14c., entunen "sing, chant, recite, vocalize," from Old French entoner "to sing, chant" (13c.), from Medieval Latin intonare "sing according to tone," from Latin in- "in" (see in- (2)) + tonus "tone," from Greek tonos (see tenet). Related: Intoned; intoning.
intoxicate (v.): mid-15c., "to poison" (obsolete), from Medieval Latin intoxicatus, past participle of intoxicare "to poison," from in- "in" (see in- (2)) + Latin toxicare "to poison," from toxicum "poison" (see toxic). Meaning "make drunk" first recorded 1570s (implied in intoxicated). Figurative sense "excite to a high pitch of feeling" is attested from 1590s. Related: Intoxicating.
intra-: word-forming element meaning "within, inside, on the inside," from Latin preposition intra "on the inside, within, in, into;" of time, "during, in the course of," related to inter "between," from PIE *en-t(e)ro-, from root *en "in" (see in). Commonly opposed to extra-, and compare inter-. The use of intra as a prefix was rare in classical Latin.
mens sana in corpore sano: c. 1600, Latin, literally "a sound mind in a sound body," a line found in Juvenal, "Satires," x.356.
Mens sana in corpore sano is a contradiction in terms, the fantasy of a Mr. Have-your-cake-and-eat-it. No sane man can afford to dispense with debilitating pleasures; no ascetic can be considered reliably sane. Hitler was the archetype of the abstemious man. When the other krauts saw him drink water in the Beer Hall they should have known he was not to be trusted. [A.J. Liebling, "Between Meals," 1962]
mother-in-law (n.): mid-15c., "mother of one's spouse," from mother (n.1) + in-law. Also in early use, "stepmother." In British slang c. 1884, mother-in-law was "a mixture of ales old and bitter."
post-impressionism (n.): 1910, from post- + impressionism.
Post-it (n.): 1975, proprietary name.
comme il faut: 1756, French, literally "as it should be;" from comme "as, like, how," from Old French com, from Vulgar Latin quomo, from Latin quomodo "how? in what way?," pronominal adverb of manner, related to quam "how much?," qui "who" (see who).
Istanbul: Turkish name of Constantinople; it developed in Turkish 16c. as a corruption of Greek phrase eis tan (ten) polin "in (or to) the city," which is how the local Greek population referred to it. 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 -bolu.
stand-in (n.): "one who substitutes for another," 1928, from the verbal phrase, attested from 1904 in show business slang in the sense "to substitute, to fill the place of another," from stand (v.) + in (adv.).
seven-year itch (n.): 1899, American English, some sort of skin condition (sometimes identified with poison ivy infection) that either lasts seven years or returns every seven years. Jocular use for "urge to stray from marital fidelity" is attested from 1952, as the title of the Broadway play (made into a film, 1955) by George Axelrod (1922-2003), in which the lead male character reads an article describing the high number of men have extra-marital affairs after seven years of marriage.
sit-in: 1936, in reference to session musicians; 1937, in reference to union action; 1941, in reference to student protests. From the verbal phrase; see sit (v.) + in (adv.). To sit in is attested from 1868 in the sense "attend, be present;" from 1919 specifically as "attend as an observer."
stick-in-the-mud (n.): 1852, from verbal phrase, stick (v.) on notion of "one who sticks in the mud," hence "one who is content to remain in an abject condition." The phrase appears in 1730, in city of London court records, as the alias of an accused named John Baker, who with two other men received a death sentence at the Old Bailey in December 1733 for "breaking open the House of Mr. Thomas Rayner, a Silversmith, and stealing thence Plate to a great Value."
-ise: see -ize.
-ize: word-forming element used to make verbs, Middle English -isen, from Old French -iser, from Late Latin -izare, from Greek -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached.

English picked up the French form, but partially reverted to the correct Greek -z- spelling from late 16c. In Britain, despite the opposition to it (at least formerly) of OED, Encyclopaedia Britannica, the "Times of London," and Fowler, -ise remains dominant. Fowler thinks this is to avoid the difficulty of remembering the short list of common words not from Greek which must be spelled with an -s- (such as advertise, devise, surprise).
well-intentioned (adj.): 1590s, from well (adv.) + intentioned "having intentions" (of a specified kind).
Idaho: 1861 as a place name, originally applied by U.S. Congress to a proposed territorial division centered in what is now eastern Colorado; said at the time to mean "Gem of the Mountains" but probably rather from Kiowa-Apache (Athabaskan) idaahe "enemy," a name applied by them to the Comanches. Modern Idaho was organized 1861 as a county in Washington Territory; in 1863 became a territory in its own right and it was admitted as a state in 1890.
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.
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.
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).
inadvertently (adv.): 1670s, from inadvertent + -ly (2). "Inattentively, carelessly," hence "unintentionally."
Rhode Island: U.S. state, the region is traditionally said to have been named by Italian explorer Giovanni da Verrazzano when he passed through in 1524, based on an imagined similarity between modern Block Island and the Greek Isle of Rhodes. More likely from Roodt Eylandt, the name Dutch explorer Adriaen Block gave to Block Island c. 1614, literally "red island," so called for the color of its cliffs. Under this theory, the name was altered by 17c. English settlers by influence of the Greek island name (see Rhodes), and then extended to the mainland part of the colony. Block Island later (by 1685) was renamed for the Dutch explorer.
Ellis Island: sandy island in mouth of Hudson River, said to have been called "Gull Island" by local Indians and "Oyster Island" by the Dutch, renamed "Gull Island" after the British took over, then "Gibbet Island" because pirates were hanged there. Sold to Samuel Ellis in 1785, who made it a picnic spot and gave it his name. Sold by his heirs in 1808 to New York State and acquired that year by the U.S. War Department for coastal defenses. Vacant after the American Civil War until the government opened an immigration station there in 1892 to replace Castle Island.
ad infinitum: "endlessly," Latin, literally "to infinity" from ad "to" (see ad-) + infinitum "infinity," neuter of adjective infinitus "endless" (see infinite). English version to infinity is attested from 1630s.
ab initio: c. 1600, Latin, literally "from the beginning," from ab "from" + oblique case of initium "entrance, beginning," related to verb inire "to go into, enter upon, begin" (see initial).
all-inclusive (adj.): 1813, from all + inclusive. Related: All-inclusively; all-inclusiveness.
self-image (n.): also self-image, 1904 in psychology, from self- + image (n.).
self-important (adj.): "having or showing an exaggerated estimation of one's own importance," 1728, from self- + important. Related: Self-importance (1728).
self-improvement (n.): also self improvement, 1748, from self- + improvement.
self-indulgence (n.): also self indulgence, 1753, from self- + indulgence.
self-inflict (v.): 1784, from self- + inflict. Related: self-inflicted.
self-interest (n.): also self interest, 1640s, from self- + interest (n.). Related: Self-interested.
[Self-interest] is a doctrine not very lofty, but clear and sure. It does not seek to attain great objects; but it attains those it aims for without too much effort. ... [It] does not produce great devotion; but it suggests little sacrifices each day; by itself it cannot make a man virtuous; but it forms a multitude of citizens who are regulated, temperate, moderate, farsighted, masters of themselves; and if it does not lead directly to virtue through the will, it brings them near to it insensibly through habits. [Alexis de Tocqueville, "Democracy in America"]
buy-in (v.): verbal phrase, "to purchase a commission or stock," 1826, from buy (v.) + in (adv.). As a noun by 1970.
go-it-alone (adj.): attested by 1953 (in reference to U.S. foreign policy proposals), from an American English verbal phrase attested by 1842 and meaning "do anything without assistance." Go it as colloquial for "to act" (especially in a determined or vigorous way) is from 1825; hence also American English go it blind (1842) in reference to something done without regard for consequences.
inchworm (n.): also inch-worm, 1844, American English, from inch (v.) + worm (n.). Other old names for it included loaper caterpiller, measuring worm, and surveyor. All are from its mode of progress.
indicia (n.): "indications, discriminating marks," Latin plural of indicium "a notice, information, disclosure, discovery," from index (genitive indicis); see index (n.).
Ian: masc. proper name, Scottish form of John (q.v.).
incent (v.): by 1992, U.S. government-speak, a back-formation from incentive. Related: Incented; incenting. Compare incentivize.
sister-in-law (n.): mid-15c.; see sister + in-law.
intertidal (adj.): also inter-tidal, "between the high and low water marks," 1853, from inter- + tidal (adj.).
invision (n.): "want of vision," 1640s, from in- (1) "not, opposite of" + vision (n.).
invitee (n.): 1837, from invite (v.) + -ee.
ither (adj., pron.): Scottish dialectal form of other.