Online Etymology Dictionary

clitoris (n.): 1610s, coined in Modern Latin from Late Greek kleitoris, a diminutive, but the exact sense is uncertain. Perhaps from Greek kleiein "to sheathe," also "to shut," in reference to its being covered by the labia minora. The related Greek noun form kleis has a second meaning of "a key, a latch or hook (to close a door);" see close (v.), and cf. slot (n.2).

Some ancient medical sources give a supposed Greek verb kleitoriazein "to touch or titillate lasciviously, to tickle" (cf. German slang der Kitzler "clitoris," literally "the tickler"), but the verb is likely from the anatomy in this case. Perhaps related to Greek kleitys, a variant of klitys "side of a hill," itself related to klinein "to slope," from the same root as climax (see lean (v.)), and with a sense of "little hill." The anatomist Mateo Renaldo Colombo (1516-1559), professor at Padua, claimed to have discovered it ("De re anatomica," 1559, p. 243). He called it amor Veneris, vel dulcedo "the love or sweetness of Venus." It had been known earlier to women.
cloaca (n.): 1650s, Modern Latin, euphemism for "sewer," from Latin cloaca "sewer, drain," from cluere "to cleanse," from PIE root *kleue- "to wash, clean" (cf. Greek klyzein "to dash over, wash off, rinse out," klysma "liquid used in a washing;" Lithuanian šluoju "to sweep;" Old English hlutor "pure, clear"). Related: Cloacinal.
cloak (n.): late 13c., from Old North French cloque (Old French cloche) "travelling cloak," from Medieval Latin clocca "travelers' cape," literally "a bell," so called from the garment's bell-like appearance (see bell (n.); the word is thus a doublet of clock (n.)). Cloak and dagger (1806) translates French de cape et d'épée.
cloak (v.): c.1500, from cloak (n.). Related: Cloaked; cloaking.
cloakroom (n.): 1852, from cloak (n.) + room (n.).
clobber (v.): 1941, British air force slang, probably related to bombing; possibly echoic. Related: Clobbered; clobbering. In late 19c. British slang the word principally had to do with clothing, e.g. clobber (n.) "clothes," (v.) "to dress smartly;" clobber up "to patch old clothes for reuse."
cloche (n.): type of bell jar, 1882, from French cloche "bell, bell glass," 12c., from Late Latin clocca (see clock (n.)). As a type of women's hat, recorded from 1907, so called from its shape.
clock (n.): late 14c., clokke, originally "clock with bells," probably from Middle Dutch clocke (Dutch klok), from Old North French cloque, from Medieva Latin (7c.) clocca "bell," probably from Celtic (cf. Old Irish clocc, Welsh cloch "bell") and spread by Irish missionaries (unless the Celtic words are from Latin); ultimately of imitative origin. Replaced Old English dægmæl, from dæg "day" + mæl "measure, mark." The Latin word was horologium; the Greeks used a water-clock (klepsydra, literally "water thief").
clock (v.): "to time by the clock," 1883, from clock (n.). The slang sense of "hit, sock" is 1941, originally Australian, probably from earlier slang clock (n.) "face" (1923).
clockwise (adv.): also clock-wise, 1879, from clock (n.) + wise (n.).
clockwork (n.): 1660s, "mechanism of a clock," from clock (n.) + work (n.). Figurative sense of "anything of unvarying regularity" is recorded earlier (1620s).
clod (n.): "lump of earth or clay," Old English clod- (in clod-hamer "field-goer"), from Proto-Germanic *kludda-, from PIE *gleu- (see clay). Synonymous with clot until 18c. Meaning "person" ("mere lump of earth") is from 1590s; that of "blockhead" is from c.1600. It also was a verb in Middle English, meaning both "to coagulate, form into clods" and "to break up clods after plowing."
clodhopper (n.): 1690s, slang, "one who works on plowed land," from clod (n.) + agent noun from hop (v.). Perhaps a play on grasshopper. Sense extended by 1836 to the shoes worn by such workers.
clog (n.): early 14c., clogge "a lump of wood," origin unknown. Also used in Middle English of large pieces of jewelry and large testicles. The sense of "wooden-soled shoe" is first recorded late 14c., probably originally meaning the wooden sole itself.
clog (v.): late 14c., "hinder," originally by fastening a block of wood to something, from clog (n.). Meaning "choke up" is 17c. Related: Clogged; clogging.
cloisonne (adj.): 1863, "divided into compartments," from French cloisonné, from cloison "a partition" (12c., in Old French, "enclosure"), from Provençal clausio, from Latin noun of action from clausus "shut" (see clause).
cloister (n.): early 13c., from Old French cloistre "monastery, convent" (12c., Modern French cloître) or Old English clauster, both from Medieval Latin claustrum "portion of monastery closed off to laity," from Latin claustrum "place shut in, enclosure; bar, bolt, means of shutting in," from past participle stem of claudere (see close (v.)). Sense of "enclosed space" extended to "place of religious seclusion."
cloister (v.): c.1400 (implied in cloistered), from cloister (n.). Related: Cloistered; cloistering.
clomp (v.): "to walk as with clogs," 1829, probably a variant of clump (v.). Related: Clomped; clomping.
clone (n.): 1903, in botany, from Greek klon "a twig, spray," related to klados "sprout, young branch, offshoot of a plant," possibly from PIE root *kel- "to strike, cut" (see holt).
clone (v.): 1959, from clone (n.). Related: Cloned; cloning. Extension to genetic duplication of human beings is from 1970.
clonus (n.): "violent muscular spasms," 1817, from Modern Latin, from Greek klonos "turmoil, violent motion, confusion, tumult," from PIE *kel- "to drive, set in motion."
Clootie (n.): "the devil," late 18c., Scottish, literally "hoofed," from cloot "hoof," from Old Norse klo "claw" (see claw (n.)).
clop (v.): 1901, echoic of the sound of boots or hoofs on the ground. Related: Clopped; clopping.
Cloris: fem. proper name, from Chloris, Latin form of Greek Khloris, goddess of flowers (later identified with Roman Flora), literally "greenness, freshness," related to khloe "young green shoot" (see Chloe).
close (v.): c.1200, "to shut, cover in," from Old French clos- (past participle stem of clore "to shut, to cut off from"), 12c., from Latin clausus, past participle of claudere "to shut, close; to block up, make inaccessible; put an end to; shut in, enclose, confine," from PIE root *klau- "hook, crooked or forked branch" (used as a bar or bolt in primitive structures); cf. Latin clavis "key," clavus "nail," claustrum "bar, bolt, barrier," claustra "dam, wall, barricade, stronghold;" Greek kleidos (genitive) "bar, bolt, key," klobos "cage;" Old Irish clo "nail," Middle Irish clithar "hedge, fence;" Old Church Slavonic ključi "hook, key," ključiti "shut;" Lithuanian kliuti "to catch, be caught on," kliaudziu "check, hinder," kliuvu "clasp, hang;" Old High German sliozan "shut," German schließen "to shut," Schlüssel "key." Also partly from Old English beclysan. Related: Closed; closing.
close (adj.): late 14c., "strictly confined," also "secret," from Old French clos "confined; concealed, secret; taciturn" (12c.), from Latin clausus, past participle of claudere "stop up, fasten, shut" (see close (v.)); main sense shifting to "near" (late 15c.) by way of "closing the gap between two things." Related: Closely. Close call is 1881; close shave is 1834. Close-up (n.) in photography, etc., is from 1913. Close-minded is attested from 1818.
close (n.): late 14c., from close (v.).
close quarters: 1753, originally nautical, and reflecting the confusion of close (v.) and close (adj.); "now understood of proximity, but orig. 'closed' space on ship-board where last stand could be made against boarders" [Weekley]. Cf. also closed-minded, a variant of close-minded attested from 1880s, with a sense of "shut" rather than "tight."
closed (adj.): past participle adjective from close (v.). Closed circuit is attested from 1827; closed shop in union sense from 1904; closed system first recorded 1896 in William James.
closet (n.): late 14c., from Old French closet "small enclosure, private room," diminutive of clos, from Latin clausum "closed space," from neuter past participle of claudere "to shut" (see close (v.)). In Matt. vi:6 it renders Latin cubiculum "bedchamber, bedroom," Greek tamieion "chamber, inner chamber, secret room;" thus originally in English "a private room for study or prayer." Modern sense of "small side-room for storage" is first recorded 1610s.

The adjective is from 1680s, "private, secluded;" meaning "secret, unknown" recorded from 1952, first of alcoholism, but by 1970s used principally of homosexuality; the phrase come out of the closet "admit something openly" first recorded 1963, and lent new meanings to the word out.
closure (n.): late 14c., "a barrier, a fence," from Old French closure "enclosure; that which encloses, fastening, hedge, wall, fence," also closture "barrier, division; enclosure, hedge, fence, wall" (12c., Modern French clôture), from Latin clausura "lock, fortress, a closing" (source of Italian chiusura), from past participle stem of claudere "to close" (see close (v.)). Sense of "act of closing, bringing to a close" is from early 15c. Sense of "tendency to create ordered and satisfying wholes" is 1924, from Gestalt psychology.
clot (n.): Old English clott, akin to Dutch kloot "ball," German Klotz "lump, block;" probably related to cleat and clod.
clot (v.): early 15c., from clot (n.). Of fluids from 1590s. Related: Clotted; clotting.
cloth (n.): Old English clað "a cloth, woven or felted material to wrap around one," hence, "garment," from Proto-Germanic *kalithaz (cf. Old Frisian klath, Middle Dutch cleet, Dutch kleed, Middle High German kleit, German Kleid "garment"), of obscure origin. The cloth "the clerical profession" is from 17c.
clothe (v.): Old English claþian, from clað (see cloth). Related: Clothed. Other Old English words for this were scrydan and gewædian.
clothes (n.): Old English claðas "cloths, clothes," originally plural of clað "cloth" (see cloth), which, in 19c., after the sense of "article of clothing" had faded from it, acquired a new plural form, cloths, to distinguish it from this word.
clothes horse (n.): also clothes-horse, "upright wooden frame for hanging clothes to dry," 1788, from clothes + horse. Figurative sense of "person whose sole function seems to be to show off clothes" is 1850.
clothesline (n.): 1830, from clothes + line (n.). As a kind of high tackle in U.S. football (the effect is similar to running into a taut clothesline) attested by 1970; as a verb by 1959.
clothespin (n.): also clothes-pin, by 1835, American English, from clothes + pin (n.).
clothier (n.): mid-15c. (late 13c. as a surname) Middle English agent noun from cloth; also see -ier.
clothing (n.): c.1200, verbal noun from clothe.
cloture (n.): 1871, the French word for "the action of closing," applied to debates in the French Assembly, then to the House of Commons and U.S. Congress, from French clôture, from Old French closture (see closure).
In foreign countries the Clôture has been used notoriously to barricade up a majority against the "pestilent" criticism of a minority, and in this country every "whip" and force is employed by the majority to re-assert its continued supremacy and to keep its ranks intact whenever attacked. How this one-sided struggle to maintain solidarity can be construed into "good for all" is inexplicable in the sense uttered. ["The clôture and the Recent Debate, a Letter to Sir J. Lubbock," London, 1882]
cloud (n.): Old English clud "mass of rock," related to clod. Metaphoric extension 13c. based on similarity of cumulus clouds and rock masses. The usual Old English word for "cloud" was weolcan. In Middle English, skie also originally meant "cloud." The four fundamental types of cloud classification (cirrus, cumulus, stratus, nimbus) were proposed by British amateur meteorologist Luke Howard (1772-1864) in 1802.
cloud (v.): early 15c., from cloud (n.). Related: Clouded; clouding.
Cloud Cuckoo Land: Imaginary city built in air, translating Aristophanes' Nephelokokkygia in "The Birds" (414 B.C.E.).
cloud nine (n.): by 1950, sometimes also cloud seven (1956, perhaps by confusion with seventh heaven), American English, of uncertain origin or significance. Some connect the phrase with the 1895 International Cloud-Atlas (Hildebrandsson, Riggenbach and Teisserenc de Bort), long the basic source for cloud shapes, in which, of the ten cloud types, cloud No. 9, cumulonimbus, was the biggest, puffiest, most comfortable-looking. Shipley suggests the sense in this and other expressions might be because, "As the largest one-figure integer, nine is sometimes used for emphasis." The phrase might appear in the 1935 aviation-based play "Ceiling Zero" by Frank Wilbur Wead.
cloudburst (n.): 1817, American English, from cloud (n.) + burst (n.). Parallels German Wolkenbruch.
cloudy (adj.): Old English cludig "rocky, full of cliffs;" see cloud (n.). Meaning "of the nature of clouds" is recorded from c.1300; meaning "full of clouds" is late 14c.; that of "not clear" is from 1580s. Figurative sense of "gloomy" is late 14c. Related: Cloudiness.
clough (n.): "ravine with a river," Old English cloh (in place names), of uncertain origin.