Online Etymology Dictionary

clue (n.): 1590s, spelling variant of clew "a ball of thread or yarn," in this sense with reference to the one Theseus used as a guide out of the Labyrinth. The purely figurative sense of "that which points the way" is from 1620s. As something which a bewildered person does not have, by 1948.
clue (v.): "to inform someone of the important facts," usually with in, 1934, from clue (n.). Related: Clued; cluing. Earlier in now-obsolete sense of "follow or track by clues" (1660s). In nautical use, "to haul up (a sail) by means of the clue-lines," from clue (n.) in the "wound ball of yarn" sense.
clueless (adj.): 1862, "trackless," from clue (n.) + -less. Meaning "ignorant, uninformed" is from 1943, said to be RAF slang from 1930s. Student slang use by 1985 is perhaps an independent extension along the same line. Related: Cluelessly; cluelessness.
clump (n.): 1580s, "lump; cluster of trees," from Middle English clompe "a lump" (c. 1300), from Dutch klomp "lump, mass," or Middle Low German klumpe "clog, wooden shoe." Old English had clympre "lump, mass of metal."
clump (v.2): "walk heavily," 1660s, imitative. Related: Clumped; clumping.
clump (v.1): "to heap or gather in clumps" (transitive), 1824, from clump (n.). Related: Clumped; clumping. Intransitive sense "to form a clump or clumps" is recorded from 1896.
clumperton (n.): "clown, clodhopper," 1530s, from clump (n.), probably on model of simpleton.
clumpy (adj.): 1820, from clump (n.) + -y (2). Also noted 1881 in an Isle of Wight glossary as a noun meaning "a stupid fellow." Related: Clumpily; clumpiness. Compare also clumperton "clown, clodhopper" (1530s).
clumsy (adj.): 1590s, "acting as if benumbed," alteration of Middle English clumsid "numb with cold" (14c.), past participle of clumsen "to benumb, stiffen or paralyze with cold or fear," from a Scandinavian source akin to Old Norse klumsa "make speechless, palsy; prevent from speaking," intensive of kluma "to make motionless." For insertion of -s-, see flimsy.

Not in general use until 18c., with senses "manifesting awkwardness; so made as to be unwieldy." Related: Clumsily; clumsiness. Compare Swedish dialectal klummsen "benumbed with cold," Norwegian klumsad (past participle) "speechless, palsied by a spasm or by fear or witchery;" German verklammen "grow stiff or numb with cold." Also compare clumse (n.) "a stupid fellow."
clung: Old English clungen, past tense and past participle of cling.
clunk (v.): 1796, "to make the sound of a cork being pulled from a bottle;" imitative. This was the main sense through most of 19c. Meaning "to hit, strike" is attested from 1940s. Related: Clunked; clunking.
clunker (n.): "anything inferior," 1940s, agent noun from clunk (v.), probably in imitation of the sounds made by old machinery. Specific sense of "old car" was in use by 1951 (clunk in the sense "old worn-out machine" is from 1940s).
clunky (adj.): "blocky, ungraceful," by 1968 (when it was the name of a style of women's shoe), from clunk + -y (2). Related: Clunkily; clunkiness.
cluster (n.): Old English clyster "cluster," probably from the same root as clot (n.). Of stars, from 1727. Cluster-bomb attested from 1967.
cluster (v.): late 14c. (transitive), from cluster (n.). Intransitive sense from 1540s. Related: Clustered; clustering.
clusterfuck (n.): "bungled or confused undertaking," 1969, U.S. military slang, from cluster + fuck, probably in the "bungle" sense. Earlier the compound meant "orgy" (1966).
clutch (v.): Old English clyccan "bring together, bend (the fingers), clench," from PIE *klukja- (source also of Swedish klyka "clamp, fork;" related to cling). Meaning "to grasp" is early 14c.; that of "to seize with the claws or clutches" is from late 14c. Sense of "hold tightly and close" is from c. 1600. Influenced in meaning by Middle English cloke "a claw." Related: Clutched; clutching.
clutch (n.3): "a brood, a nest" in reference to chickens, eggs, 1721, from clekken "to hatch" (c. 1400). Said by OED to be apparently a southern England dialect word. Compare batch/bake. Probably from a Scandinavian source (such as Old Norse klekja "to hatch"), perhaps of imitative origin (compare cluck (v.)).
clutch (n.2): movable mechanical part for transmitting motion, 1814, from clutch (v.), with the "seizing" sense extended to "device for bringing working parts together." Originally of mill-works, first used of motor vehicles 1899. Meaning "moment when heroics are required" is attested from 1920s.
clutch (n.1): "a claw, grip, grasp," c. 1300, from cloche "claw," from cloke (c. 1200), related to clucchen, clicchen (see clutch (v.)). Meaning "grasping hand" (1520s) led to that of "tight grasp" (1784). Related: Clutches.
clutter (v.): 1550s, "to collect in heaps," variant of clotern "to form clots, to heap on" (c. 1400); related to clot (n.). Sense of "to litter" is first recorded 1660s. Related: Cluttered; cluttering.
clutter (n.): 1570s, "things lying in heaps or confusion," from clutter (v.); the "litter" sense is from 1660s.
Clyde: masc. proper name, from the family name, from the region of the Clyde River in Scotland (see Clydesdale). Most popular in U.S. for boys c. 1890-1910, falling off rapidly thereafter, hence probably its use in 1940s teenager slang for "a square, one not versed in popular music or culture."
Clydesdale: "breed of heavy draught horses," 1786, so called because they were bred in the valley of the Clyde in Scotland. The river name is perhaps literally "cleansing," from a Celtic root akin to Latin cloaca (see cloaca).
clyster (n.): from French clystère (Old French clistre, 13c.) or directly from Latin clyster, from Greek klyster, from klyzein "to wash out" (see cloaca).
Clytaemnestra: also Clytemnestra, wife and murderess of Agamemnon, from Greek Klytaimnestra, from klytos "celebrated, heard of" (see loud) + mnester "wooer, suitor," literally "willing to mind, mindful of," related to mnasthai "to remember," from PIE root *men- "to think" (see mind (n.)).
cn-: consonant group used in Old English (the Clark Hall dictionary has 82 entries under cn-) but in Middle English all lost or turned to kn-. Also common in Greek, and retained in the spelling of some English words from Greek but not now admitted in speech, the n- only being sounded.
Cnidaria (n.): phylum of stinging invertebrates, from Latinized form of Greek knide "nettle," from stem of knizein "to scratch scrape," + abstract noun ending -ia. Related: Cnidarian.
co-: in Latin, the form of com- in compounds with stems beginning in vowels and h- and gn- (see com-). Taken in English from 17c. as a living prefix meaning "together, mutually, in common," and used promiscuously with native words and Latin-derived words not beginning with vowels, sometimes even with words already having it (such as co-conspiritor).
co-ed (n.): also coed, 1886, American English, (first in Louisa Mae Alcott's "Jo's Boys"); short for "co-educational system;" 1889 as an adjective, short for coeducational; 1893 as a noun meaning "girl or woman student at a co-educational institution."
co-op (n.): 1861, abbreviation of cooperative. The hyphen is needed to avoid confusion with coop (n.).
co-opt (v.): 1650s, "to select (someone) for a group or club by a vote of members," from Latin cooptare "to elect, to choose as a colleague or member of one's tribe," from com- "together" (see com-) + optare "choose" (see option (n.)). For some reason this defied the usual pattern of Latin-to-English adaptation, which should have yielded *cooptate. Sense of "take over" is first recorded c. 1953. Related: Co-opted; co-opting.
co-ordinate: see coordinate.
co-star: also costar, 1919 as a verb; 1926 as a noun, from co- + star (v.).
co.: abbreviation of company, attested by 1670s.
coach (n.): 1550s, "large kind of carriage," from Middle French coche (16c.), from German kotsche, from Hungarian kocsi (szekér) "(carriage) of Kocs," village where it was first made. In Hungary, the thing and the name for it date from 15c., and forms are found in most European languages (Spanish and Portuguese coche, Italian cocchino, Dutch koets). Applied to railway cars 1866, American English. Sense of "economy or tourist class" is from 1949. Meaning "instructor/trainer" is c. 1830 Oxford University slang for a tutor who "carries" a student through an exam; athletic sense is 1861.
coach (v.): 1610s, "to convey in a coach," from coach (n.). Meaning "to prepare (someone) for an exam" is from 1849. Related: Coached; coaching.
coachman (n.): 1570s, from coach (n.) + man (n.).
coagulant (n.): 1770, from Latin coagulantem (nominative coagulans), present participle of coagulare (see coagulate).
coagulate (v.): early 15c., from Latin coagulatus, past participle of coagulare "to cause to curdle," from cogere "to curdle, collect" (see cogent). Earlier coagule, c. 1400, from Middle French coaguler. Related: Coagulated; coagulating.
coagulation (n.): c. 1400, from Latin coagulationem (nominative coagulatio), noun of action from past participle stem of coagulare (see coagulate).
coal (n.): Old English col "charcoal, live coal," from Proto-Germanic *kula(n) (source also of Old Frisian kole, Middle Dutch cole, Dutch kool, Old High German chol, German Kohle, Old Norse kol), from PIE root *g(e)u-lo- "live coal" (source also of Irish gual "coal").

Meaning "mineral consisting of fossilized carbon" is from mid-13c. First mentioned (370 B.C.E.) by Theophrastus in his treatise "On Stones" under the name lithos anthrakos (see anthrax). Traditionally good luck, coal was given as a New Year's gift in England, said to guarantee a warm hearth for the coming year. The phrase drag (or rake) over the coals was a reference to the treatment meted out to heretics by Christians. To carry coals "do dirty work," also "submit to insult" is from 1520s. To carry coals to Newcastle "add to that of which there is already an abundance" (c. 1600) is a local variant on an ancient class of expression: Latin had in litus harenas fundere "pour sand on the beach;" Greek glauk eis Athenas "owls to Athens."
coalesce (v.): 1540s, from Latin coalescere "unite, grow together, become one in growth," from com- "together" (see co-) + alescere "to grow up" (see adolescent). Related: Coalesced; coalescing; coalescence; coalescent.
coalition (n.): 1610s, "the growing together of parts," from French coalition (1540s), from Late Latin coalitus "fellowship," originally past participle of Latin coalescere "unite, grow together, become one in growth" (see coalesce). First used in a political sense 1715.
coaming (n.): 1610s, nautical, of unknown origin.
coarse (adj.): early 15c., cors "ordinary" (modern spelling is from late 16c.), probably adjectival use of noun cours (see course (n.)), originally referring to rough cloth for ordinary wear. Developed a sense of "rude" c. 1500 and "obscene" by 1711. Perhaps related, via metathesis, to French gros, which had a similar sense development. Related: Coarsely; coarseness.
coarsen (v.): 1805, from coarse + -en (2). Related: Coarsened; coarsening.
coast (n.): "margin of the land," early 14c.; earlier "rib as a part of the body" (early 12c.), from Old French coste "rib, side, flank; slope, incline;" later "coast, shore" (12c., Modern French côte), from Latin costa "a rib," perhaps related to a root word for "bone" (compare Old Church Slavonic kosti "bone," also see osseous).

Latin costa developed a secondary sense in Medieval Latin of "the shore," via notion of the "side" of the land, as well as "side of a hill," and this passed into Romanic (Italian costa "coast, side," Spanish cuesta "slope," costa "coast"), but only in the Germanic languages that borrowed it is it fully specialized in this sense (Dutch kust, Swedish kust, German Küste, Danish kyst). French also used this word for "hillside, slope," which led to verb meaning "sled downhill," first attested 1775 in American English. Expression the coast is clear (16c.) is an image of landing on a shore unguarded by enemies.
coast (v.): late 14c., "to skirt, to go around the sides, to go along the border" of something (as a ship does the coastline), from Anglo-French costien, from the French source of coast (n.). The meaning "sled downhill," first attested 1775 in American English, is a separate borrowing. Of motor vehicles, "to move without thrust from the engine," by 1925; figurative use, of persons, "not to exert oneself," by 1934. Related: Coasted; coasting.
coastal (adj.): 1883, from coast (n.) + -al (1). The proper Latin form costal is used only of ribs.