Online Etymology Dictionary

Kevlar: registered trademark (DuPont) for a synthetic fiber developed there c. 1965; probably an invented word of no etymology.
kew: 1939, as a clipped form of thank you.
kewl: 1996 as a graphic representation of a casual pronunciation of cool (adj.).
kewpie (n.): 1909, American English, coined by their inventor and illustrator, Rose C. O'Neill (1874-1944), as an altered form of a diminutive of Cupid. Kewpie doll is from 1916.
kex (n.): "dry, hollow plant stem," early 14c., of uncertain origin. Klein says ultimately from Latin cicuta "hemlock."
key (n.1): "instrument for opening locks," Middle English keie, from Old English cæg "metal piece that works a lock, key" literal and figurative ("solution, explanation, one who or that which opens the way or explains"), a word of unknown origin, abnormal evolution, and no sure cognates other than Old Frisian kei.

Perhaps it is related to Middle Low German keie "lance, spear" on notion of "tool to cleave with," from Proto-Germanic *ki- "to cleave, split" (cognates: German Keil "wedge," Gothic us-kijans "come forth," said of seed sprouts, keinan "to germinate"). But Liberman writes, "The original meaning of *kaig-jo- was presumably '*pin with a twisted end.' Words with the root *kai- followed by a consonant meaning 'crooked, bent; twisted' are common only in the North Germanic languages." Compare also Sanskrit kuncika- "key," from kunc- "make crooked."

Modern pronunciation is a northern variant predominating from c. 1700; earlier and in Middle English it often was pronounced "kay." Meaning "that which holds together other parts" is from 1520s. Meaning "explanation of a solution" (to a set problem, code, etc.) is from c.1600.

The musical sense originally was "tone, note" (mid-15c.). In music theory, the sense developed 17c. to "sum of the melodic and harmonic relationships in the tones of a scale," also "melodic and harmonic relationships centering on a given tone." Probably this is based on a translation of Latin clavis "key," used by Guido for "lowest tone of a scale," or French clef (see clef; also see keynote). Sense of "mechanism on a musical instrument operated by the player's fingers" is from c. 1500, probably also suggested by uses of clavis. OED says this use "appears to be confined to Eng[lish]." First of organs and pianos, by 1765 of wind instruments; transferred to telegraphy by 1837 and later to typewriters (1876).
key (n.2): "low island," 1690s, from Spanish cayo "shoal, reef," from Taino cayo "small island;" spelling influenced by Middle English key "wharf" (c. 1300; mid-13c. in place names), from Old French kai "sand bank" (see quay).
key (adj.): "crucially important," 1913, from key (n.1). Perhaps from or reinforced by key move, in chess, "first move in a solution to a set problem" (1827), which to an experienced player opens the way to see how the solution will develop.
key (v.): mid-14c., "fasten with a wedge or key" (implied in keyed), from key (n.1). From 1630s as "regulate the pitch of a musical instrument by means of a key," also in the figurative sense "give a tone or intensity to." From 1963 as "do data entry or other work on a keyboard." Meaning "to scratch (a car's paint job) with a metal key" is recorded by 1986. Related: Keyed; keying.
keyboard (n.): 1819, from key (n.1) in sense of "mechanism of a musical instrument" + board (n.1). Originally of pianos, organs, etc., extended to other machines 1846. The verb is first recorded 1926 (implied in keyboarding).
keychain (n.): also key-chain, 1849, from key (n.1) + chain (n.). Earlier in the same sense was key-ring (1889), key-band (mid-15c.).
keyed (adj.): 1796, "having keys," from key (n.) in the musical sense. Also "to set the tone (of a musical instrument) to a particular key; hence figurative keyed up "excited, high-strung" (1889).
keyhole (n.): 1590s, from key (n.1) + hole (n.).
keyless (adj.): 1823, from key (n.1) + -less.
Keynesian: 1937 (adj.), 1942 (n.), from name of British economist John Maynard Keynes (1883-1946).
keynote (n.): also key-note, "lowest note of a musical scale, basis of a tonal key, the tonic," 1776, from key (n.1) in sense of "musical scale" + note (n.). The keynote is the given note on which the melodic and harmonic relationships in the scale are built, and it gives its name to the key. Figurative sense of "leading idea, central principle" is from 1783; keynote speech is 1887, American English.
keypad (n.): "handheld pad of labelled buttons to work electronics," 1975, from key (n.1) + pad (n.).
keypunch (n.): 1933, from keyboard (which operated it) + punch (v.), which is what it did to the cards inserted in it to record data.
keystone (n.): "stone in the middle of an arch (typically the uppermost stone), which holds up the others," 1630s, earlier simply key (1520s), from key (n.1) in figurative sense of "that which holds together other parts," or from its Middle English architectural sense "projecting ornament of at the intersections of ribs of vaulted or flat ceilings" (mid-14c.). Being the last put in, it is regarded as "keying," or locking together, the whole structure.

Figurative sense "chief element of a system" is from 1640s. Pennsylvania was called the Keystone State because of its position (geographical and political) in the original American confederation, occupying the middle (7th) place in the "arch" of states along the Atlantic, between eastern states and southern ones. Keystone cops were the bumbling police in the slapstick silent movies produced by Keystone Studios, formed in 1912 in Edendale, Calif., by Canadian-born U.S. film director Mack Sennett (1884-1960).
keystroke (n.): 1902, from key (n.1) + stroke (n.). Not in common use until the rise of computers. As a verb, by 1966 (implied in keystroking).
keyword (n.): also key-word, "word which serves as a guide to other words or matters," 1807, from key (n.1) in the figurative sense + word (n.). Originally in reference to codes and ciphers. In reference to information retrieval systems, "word from the text chosen as indicating the contents of a document" (1967).
Keziah: fem. proper name, biblical daughter of Job, from Hebrew Qetzi'ah, literally "cassia," the aromatic tree that produces cinnamon.
KGB: national security agency of the Soviet Union from 1954 to 1991, attested from 1955 in English, initialism (acronym) of Russian Komitet gosudarstvennoy bezopasnosti "Committee for State Security."
kh-: used to represent sounds not native to English, more or less resembling an aspirated "k," in transliterations from Arabic, Turkish, Russian, etc.
khaki (n.): "dust-colored cloth," 1857, from Urdu khaki, literally "dusty," from khak "dust," a word from Persian. Used principally at first for uniforms of British cavalry in India, introduced in the Guide Corps, 1846; widely adopted for camouflage purposes in the Boer Wars (1899-1902). It once had overtones of militarism. As an adjective from 1863. Related: Khakis.
khan (n.): title of sovereign princes in Tatar counties, c. 1400, from Turkic, literally "lord, prince," contraction of khaqan "ruler, sovereign." The word has been known in the languages of Europe since 13c.; compare Medieval Latin chanis, Medieval Greek kanes, Old French chan, Russian khanu. In time it degenerated and became a title of respect. The female form is khanum (1824), from Turkish khanim.
khanate (n.): "the dominion of a khan," 1799, from khan + -ate (1).
khatib (n.): Muslim preacher, 1620s, from Arabic, from khataba "to preach."
khedive (n.): title of the Turkish viceroy of Egypt, 1867, from French khédive, from Turkish khidiv, from Persian khidiw "prince," derivative of khuda "master, prince," from Old Persian khvadata- "lord," from compound *khvat-data-, literally "created from oneself," from khvat- (from PIE *swe-tos "from oneself," ablative of root *s(w)e-; see idiom) + data- "created." His wife was a khediva.
Khmer: 1867, native name. Khmer Rouge, communist party of Cambodia, literally "Red Khmer," is with French rouge (see rouge (n.)).
kibble (n.): "ground-up meat used as dog food, etc.," 1957, apparently from the verb meaning "to bruise or grind coarsely," which is attested from 1790, first in milling; a word of unknown origin. The same or an identical word was used in the coal trade in the late 19c. and in mining from the 1670s for "bucket used to haul up ore or waste."
kibbutz (n.): "Israeli collective settlement," 1931, from Modern Hebrew qibbus "gathering," earlier "a gathering together," verbal noun from root of qibbetz "he gathered together." Plural is kibbutzim. Related to Arabic quabada "he grasped, seized."
kibitz (v.): "a looker-on," 1920, from kibitz (v.), American English, 1915, from Yiddish kibitsen "to offer gratuitous advice as an outsider," from German kiebitzen "to look on at cards, to kibitz," originally in Rotwelsch (thieves' cant) "to visit," from Kiebitz, name of a shore bird (European pewit, lapwing) with a folk reputation as a meddler, from Middle High German gibitz "pewit," imitative of its cry. Young lapwings are proverbially precocious and active, and were said to run around with half-shells still on their heads soon after hatching. Related: Kibitzing. Also see kibitzer.
kibitzer (n.): 1915, from Yiddish, agent noun from kibitz (q.v.). Kibitz as a verb is attested in English from 1915; "Der Kibitzer" is noted as the name of a humorous Yiddish weekly published in New York 1908-1912.
kibosh (n.): 1836, kye-bosk, in British English slang phrase put the kibosh on, of unknown origin, despite intense speculation. The earliest citation is in Dickens. Looks Yiddish, but its original appearance in a piece set in the heavily Irish "Seven Dials" neighborhood in the West End of London seems to argue against this.

One candidate is Irish caip bháis, caipín báis "cap of death," sometimes said to be the black cap a judge would don when pronouncing a death sentence, but in other sources this is identified as a gruesome method of execution "employed by Brit. forces against 1798 insurgents" [Bernard Share, "Slanguage, A Dictionary of Irish Slang"]. Or the word might somehow be connected with Turkish bosh (see bosh).
kick (v.): late 14c., "to strike out with the foot," of uncertain origin, perhaps from Old Norse kikna "bend backwards, sink at the knees." "The doubts OED has about the Scandinavian origin of kick are probably unfounded" [Liberman]. Older sources guessed it to be from Celtic. Earliest in the biblical phrase that is now usually rendered as kick against the pricks. Related: Kicked; kicking.

Transitive sense "give a blow with the foot" is from 1580s. Meaning "to strike in recoiling" (as a gun, etc.) is from 1832. Figurative sense of "complain, protest, manifest strong objection, rebel against" (late 14c.) probably is at least in part from the Bible verse. Slang sense of "die" is attested from 1725 (kick the wind was slang for "be hanged," 1590s; see also bucket). Meaning "to end one's drug habit" is from 1936.

Kick in "to break (something) down" is from 1876, sense of "contribute" is from 1908, American English; kick out "expel" is from 1690s. To kick around (intransitive) "wander about" is from 1839; transitive sense of "treat contemptuously" is from 1871 on the notion of "kick in all directions." To be kicked upstairs "removed from action by ostensible promotion" is from 1750. To kick oneself in self-reproach is from 1891. The children's game of kick the can is attested from 1891.
kick (n.): 1520s, "a blow or thrust with the foot," from kick (v.). Meaning "recoil (of a gun) when fired" is from 1826. Meaning "surge or fit of pleasure" (often as kicks) is from 1941; originally "stimulation from liquor or drugs" (1844). Hence kickster "one who lives for kicks" (1963). The kick "the fashion" is from c. 1700. Kicks in slang also has meant "trousers" (1700), "shoes" (1904).
kick-ball (n.): also kickball, children's game, 1854; see kick (v.) + ball (n.1).
kick-off (n.): also kickoff, kick off, 1857, "first kick in a football match," from kick (v.) + off (adv.). The verbal phrase also is from 1857. Figurative sense of "start, beginning event" is from 1875.
Kickapoo: Native American people of the Algonquian family, 1722, from native /kiikaapoa/ which is sometimes interpreted as "wanderers" [Bright].
kickback (n.): also kick-back, "mechanical reaction in an engine," from 1905 in various mechanical senses, from the verbal phrase (1895); see kick (v.) + back (adv.). By 1926 the verbal phrase was being used in a slang sense of "be forced to return pelf, pay back to victims," which was extended to illegal partial give-backs of government-set wages that were extorted from workers by employers. Hence the noun in the sense of "illegal or improper payment" (1932). The verbal phrase in the sense "make oneself comfortable, prepare to relax" is from 1975.
kickboxing (n.): also kick-boxing, 1968, from kick (n.) + boxing (n.). Related: Kickbox (v.); kickboxer (1978).
kicker (n.): 1570s, originally of horses, agent noun from kick (v.). Kickee is recorded from 1820.
kickshaw (n.): "a fancy dish in cookery" (especially a non-native one), late 16c., earlier quelk-chose from English pronunciation of French quelque chose "a something, a little something." Quelque is from Latin qualis "of what kind?" (see quality).
kicksie-wicksie (n.): also kicksy-wicksy, ludicrous or loving term for "wife" in Shakespeare ("All's Well," II iii.297), 1601, perhaps a perversion of kickshaw "a fancy dish in cookery."
kickstand (n.): also kick-stand, "metal support for holding a bicycle upright," 1936, from kick (n.) + stand (n.). So called for the method of putting it in position.
kicky (adj.): 1790, "clever; showy, gaudy," from kick (n.) in the 18c. sense "that which is stylish" + -y (2). Meaning "full of thrills, providing kicks" is from 1968. Kickish "given to kicking" is from 1580s.
kid (n.): c. 1200, "the young of a goat," from a Scandinavian source such as Old Norse kið "young goat," from Proto-Germanic *kidjom (source also of Old High German kizzi, German kitze, Danish and Swedish kid), of uncertain origin.

Extended meaning "child" is first recorded as slang 1590s, established in informal usage by 1840s. Applied to skillful young thieves and pugilists since at least 1812. Kid stuff "something easy" is from 1913 (The phrase was in use about that time in reference to vaudeville acts or advertisements featuring children, and to child-oriented features in newspapers).

In clothing, "made of soft leather," as though from the skin of a kid, but commercially often of other skins. Hence Kid glove "a glove made of kidskin leather" is from 1680s; sense of "characterized by wearing kid gloves," therefore "dainty, delicate" is from 1856.
kid (v.): "tease playfully," 1839, earlier, in thieves' cant, "to coax, wheedle, hoax" (1811), probably from kid (n.), via notion of "treat as a child, make a kid of." Related: Kidded; kidding. Colloquial interjection no kidding! "that's the truth" is from 1914.
kidder (v.): "playful teaser," 1888, agent noun from kid (v.).