Online Etymology Dictionary

cock (n.2): in various mechanical senses, such as cock of a faucet (early 15c.) is of uncertain connection with cock (n.1), but German has hahn "cock" in many of the same senses. The cock of an old matchlock firearm is 1560s, hence half-cocked (for which see half).
cock (v.): mid-12c., cocken, "to fight;" 1570s, "to swagger;" seeming contradictory modern senses of "to stand up" (as in cock one's ear), c. 1600, and "to bend" (1898) are from the two cock nouns. The first is probably in reference to the posture of the bird's head or tail, the second to the firearm position. To cock ones hat carries the notion of "defiant boastfulness."
cock (n.1): "male chicken," Old English cocc "male bird," Old French coc (12c., Modern French coq), Old Norse kokkr, all of echoic origin. Old English cocc was a nickname for "one who strutted like a cock," thus a common term in the Middle Ages for a pert boy, used of scullions, apprentices, servants, etc.

A common personal name till c. 1500, it was affixed to Christian names as a pet diminutive, as in Wilcox, Hitchcock, etc. Slang sense of "penis" is attested since 1610s (but compare pillicock "penis," from c. 1300); cock-teaser is from 1891. A cocker spaniel (1823) was trained to start woodcocks. Cock-and-bull is first recorded 1620s, perhaps an allusion to Aesop's fables, with their incredible talking animals, or to a particular story, now forgotten. French has parallel expression coq-à-l'âne.
game-cock: cock bred for fighting or from fighting stock, 1670s, from game (n.) in the sporting and amusement sense + cock (n.1). Figurative use by 1727.
cock-a-doodle-doo: 1570s, imitative; compare French cocorico, German kikeriki, Latin cucurire, Russian kikareku, Vietnamese cuc-cu, Arabic ko-ko, etc.
cockerel (n.): "young cock," mid-15c. (late 12c. as a surname), apparently a diminutive of cock (n.1). Despite the form, no evidence that it is from French.
cockade (n.): 1709, earlier cockard (1650s), from French cocarde (16c.), fem. of cocard (Old French cocart) "foolishly proud, cocky," as a noun, "idiot, fool;" an allusive extension from coq (see cock (n.1)).
cockatoo (n.): 1610s, from Dutch kaketoe, from Malay kakatua, possibly echoic, or from kakak "elder brother or sister" + tua "old." Also cockatiel (1880), from Dutch diminutive kaketielje (1850), which is perhaps influenced by Portuguese. Spelling influenced by cock (n.1).
cockchafer (n.): from cock (n.1), in reference to its size, + chafer.
cocky (adj.): "arrogantly pert," 1768; originally "lecherous" (1540s); from cock (n.1) + -y (2). Related: Cockiness.
cocksure (adj.): 1520s, "certain," from cock (n.1) + sure (adj.). Probably "as assured as a cock." "The word was originally perfectly dignified, and habitually used in the most solemn connexions" [OED]. D.H. Lawrence playfully coined hensure as a female version (1929).
cockpit (n.): 1580s, "a pit for fighting cocks," from cock (n.1) + pit (n.1). Used in nautical sense (1706) for midshipmen's compartment below decks; transferred to airplanes (1914) and to cars (1930s).
cockeyed (adj.): 1821, "squint-eyed," perhaps from cock (v.) in some sense + eye (n.). Figurative sense of "absurd, askew, crazy" is from 1896; that of "drunk" is attested from 1926.
petcock (n.): also pet-cock, 1864, from cock (n.2); the signification of the first element is uncertain.
cocksucker (n.): 1890s, "one who does fellatio" (especially a male homosexual); 1920s as "contemptible person," American English, from cock (n.1) in phallic sense + sucker (n.). Used curiously for aggressively obnoxious men; the ancients would have recoiled at this failure to appreciate the difference between passive and active roles; Catullus, writing of his boss, employs the useful Latin insult irrumator, which means "someone who forces others to give him oral sex," hence "one who treats people with contempt."
cockscomb (n.): c. 1400, "comb or crest of a cock," from possessive of cock (n.1) + comb (n.). Meaning "cap worn by a professional fool" is from 1560s; hence "conceited fool" (1560s), a sense passing into the derivative coxcomb. As a plant name, from 1570s.
cockroach (n.): 1620s, folk etymology (as if from cock + roach) of Spanish cucaracha "chafer, beetle," from cuca "kind of caterpillar." Folk etymology also holds that the first element is from caca "excrement."
A certaine India Bug, called by the Spaniards a Cacarootch, the which creeping into Chests they eat and defile with their ill-sented dung [Capt. John Smith, "Virginia," 1624].
rooster (n.): 1772, agent noun from roost (v.); earlier roost cock, c. 1600, in sense of "the roosting bird." Favored in the U.S. originally as a puritan alternative to cock (n.) after it had acquired the secondary sense "penis" (and compare roach).
pillock (n.): 1530s, dialectal variant of Middle English pillicock (see cock (n.1)). Meaning "stupid person" is attested by 1967.
coquet (n.): "amorous, flirtatious person," 1690s, originally of both sexes (as it was in French), from French coquet (17c.), diminutive of coq "cock" (see cock (n.1)). A figurative reference to its strut or its lust. The distinction of fem. coquette began c. 1700, and use in reference to males has faded out since.
coax (v.): 1580s, originally in slang phrase to make a coax of, from earlier noun coax, cox, cokes "a fool, ninny, simpleton" (1560s); modern spelling is 1706. Origin obscure, perhaps related to cock (n.1). Related: Coaxed; coaxing.
peacock (n.): c. 1300, poucock, from Middle English po "peacock" + coc (see cock (n.)).

Po is from Old English pawa "peafowl" (cock or hen), from Latin pavo (genitive pavonis), which, with Greek taos said to be ultimately from Tamil tokei (but perhaps is imitative; Latin represented the peacock's sound as paupulo).

The Latin word also is the source of Old High German pfawo, German Pfau, Dutch pauw, Old Church Slavonic pavu. Used as the type of a vainglorious person from late 14c. Its flesh superstitiously was believed to be incorruptible (even St. Augustine credits this). "When he sees his feet, he screams wildly, thinking that they are not in keeping with the rest of his body." [Epiphanus]
John Hancock: colloquial for "signature," 1903 (sometimes, through some unexplainable error, John Henry), from the Boston merchant and rebel (1736-1793), signer of the U.S. Declaration of Independence. The extended sense is from his signing that dangerous document first or most flamboyantly.
John Hancock, president of Congress, was the first to sign the Declaration of Independence, writing his name in large, plain letters, and saying: "There; John Bull can read my name without spectacles. Now let him double the price on my head, for this is my defiance." [Hélène Adeline Guerber, "The Story of the Thirteen Colonies," New York, 1898]
The family name is attested from 1276 in Yorkshire, a diminutive (see cock (n.1)) of Hann, a very common given name in 13c. Yorkshire as a pet form of Henry or John.
chicken (n.): Old English cicen (plural cicenu) "young fowl," which by early Middle English had came to mean "young chicken," then later any chicken, from Proto-Germanic *kiukinam (source also of Middle Dutch kiekijen, Dutch kieken, Old Norse kjuklingr, Swedish kyckling, German Küken "chicken"), from root *keuk- (echoic of the bird's sound and possibly also the root of cock (n.1)) + diminutive suffixes.

Applied to the young of other bird species from early 13c. Adjective sense of "cowardly" is at least as old as 14c. (compare hen-herte "a chicken-hearted person," mid-15c.). As the name of a game of danger to test courage, it is first recorded 1953. Chicken feed "paltry sum of money" is by 1897, American English slang; literal use (it is made from the from lowest quality of grain) by 1834. Chicken lobster "young lobster," is from c. 1960s, American English, apparently from chicken in its sense of "young." Generic words for "chicken" in Indo-European tend to be extended uses of "hen" words, as hens are more numerous among domestic fowl, but occasionally they are from words for the young, as in English and in Latin pullus.
shuttlecock (n.): 1570s, from shuttle (v.) + cock (n.2).
tease (n.): 1690s, "act of teasing," from tease (v.). Meaning "one who teases" is from 1852. Specifically as short for cock-teaser, it was in use by 1976.
woodcock (n.): Old English wuducoc, from wudu (see wood (n.)) + coc (see cock (n.1)).
game (adj.2): "ready for action, unafraid, and up to the task;" probably literally "spirited as a game-cock," 1725, from game-cock "bird bred for fighting" (1670s), from game (n.) in the "sport, amusement" sense. Middle English adjectives gamesome, gamelich meant "joyful, playful, sportive."
coxswain (n.): early 14c., "officer in charge of a ship's boat and its crew," from cock "ship's boat" (from Old French coque "canoe") + swain "boy," from Old Norse sveinn "boy, servant" (see swain).
Cox: surname, from early 16c., earlier Cocks (c. 1300), in many cases from cock (n.1), which apparently was used as a personal name in Old English, also as a familiar term for a boy, later used of apprentices, servants, etc. Perhaps in some cases for the sign of an inn. In some cases perhaps from cook (n.), or Welsh coch "red."
cockatrice (n.): late 14c., from Old French cocatriz, altered (by influence of coq) from Late Latin *calcatrix, from Latin calcare "to tread" (from calx (1) "heel;" see calcaneus), as translation of Greek ikhneumon, literally "tracker, tracer."

In classical writings, an Egyptian animal of some sort, the mortal enemy of the crocodile, which it tracks down and kills. This vague sense became hopelessly confused in the Christian West, and in England the word ended up applied to the equivalent of the basilisk. A serpent hatched from a cock's egg, it was fabled to kill by its glance and could be slain only by tricking it into seeing its own reflection. Belief in them persisted even among the educated because the word was used in the KJV several times to translate a Hebrew word for "serpent." In heraldry, a beast half cock, half serpent.
cockney (n.): c. 1600, usually said to be from rare Middle English cokenei, cokeney "spoiled child, milksop" (late 14c.), originally cokene-ey "cock's egg" (mid-14c.). Most likely disentangling of the etymology is to start from Old English cocena "cock's egg" -- genitive plural of coc "cock" + æg "egg" -- medieval term for "runt of a clutch," extended derisively c. 1520s to "town dweller," gradually narrowing thereafter to residents of a particular neighborhood in the East End of London. Liberman, however, disagrees:
[I]n all likelihood, not the etymon of ME cokeney 'milksop, simpleton; effeminate man; Londoner,' which is rather a reshaping of [Old French] acoquiné 'spoiled' (participle). However, this derivation poses some phonetic problems that have not been resolved.
The accent so called from 1890, but the speech peculiarities were noted from 17c. As an adjective in this sense, from 1630s.
alectryomachy (n.): "cock-fighting," 1650s, from Greek alektryon "cock" (see alectryomancy) + -machy.
Cockaigne (n.): c. 1300, from Old French Cocaigne (12c.) "lubberland," imaginary country, abode of luxury and idleness. Of obscure origin, speculation centers on words related to cook (v.) and cake (compare Middle Dutch kokenje, a child's honey-sweetened treat; also compare Big Rock Candy Mountain). The German equivalent is Schlaraffenland.
cockamamie (adj.): American English slang word attested by 1946, popularized c. 1960, but said to be New York City children's slang from mid-1920s; perhaps an alteration of decalcomania (see decal).
cockle (n.1): type of mollusk, early 14c., from Old French coquille (13c.) "scallop, scallop shell; mother of pearl; a kind of hat," altered (by influence of coque "shell") from Vulgar Latin *conchilia, from Latin conchylium "mussel, shellfish," from Greek konkhylion "little shellfish," from konkhe "mussel, conch." Phrase cockles of the heart (1660s) is perhaps from similar shape, or from Latin corculum, diminutive of cor "heart."
cocktail (n.): first attested 1806; H.L. Mencken lists seven versions of its origin, perhaps the most durable traces it to French coquetier "egg-cup" (15c.; in English cocktay). In New Orleans, c. 1795, Antoine Amédée Peychaud, an apothecary (and inventor of Peychaud bitters) held Masonic social gatherings at his pharmacy, where he mixed brandy toddies with his own bitters and served them in an egg-cup. On this theory, the drink took the name of the cup. Used from 1920s of any mix of substances (fruit, Molotov). Cocktail party first attested 1928.
Molotov cocktail (n.): 1940, a term from Russo-Finnish War (used and satirically named by the Finns), from Molotov (from Russian molot "hammer") name taken by Vyacheslav Mikhailovich Skriabin (1890-1986), Soviet minister of foreign affairs 1939-1949.
cockle (n.2): flowering weed that grows in wheat fields, Old English coccel "darnel," used in Middle English to translate the Bible word now usually given as tares (see tare (n.1)). It is in no other Germanic language and may be from a diminutive of Latin coccus "grain, berry."
chanticleer (n.): "a cock," c. 1300, from Old French Chantecler "sing-loud" (Modern French Chanteclair), name of the cock in medieval stories of Reynard the Fox; from chanter "to sing" (see chant (v.)) + cler (see clear (adj.)).
white feather (n.): as a symbol of cowardice, 1785, said to be from the time when cock-fighting was respectable, and when the strain of game-cock in vogue had no white feathers, so that "having a white feather, is proof he is not of the true game breed" [Grose].
gobbler (n.): 1737, "turkey-cock," agent noun from gobble (v.2). As "one who eats greedily" 1755, from gobble (v.1).
alectryomancy (n.): "divination by means of a cock and grains of corn," 1680s, from Latinized form of Greek alektryon "cock" + manteia "oracle" (see -mancy). The first element is literally "warder-off, fighter," related to alexein "to ward off, drive or keep off" (see Alexander, and compare Alekto, name of one of the three Furies). Perhaps originally a personal name, applied at first to the fighting cock, then to cocks generally.
capon (n.): "a castrated cock," late Old English capun, from Latin caponem (nominative capo) "castrated cock" (also source of French chapon, Spanish capon, Italian cappone), perhaps literally "to strike off," from PIE root *(s)kep- "to cut" (see hatchet (n.)). Probably reinforced in Middle English by cognate Old North French capon.
gallinaceous (adj.): "of or resembling domestic fowl," 1783, from Latin gallinaceus "of hens, of fowls, pertaining to poultry," from gallina "hen," a fem. formation from gallus "cock," probably from PIE root *gal- (2) "to call, shout" (see call (v.)) as "the calling bird." But it also has an ancient association with Gaul (see Gallic), and some speculate that this is the source of the word, "on the assumption that the Romans became acquainted with the cock from Gaul, where it was brought by the Phoenicians" [Buck].
crest (n.): early 14c., from Old French creste "tuft, comb" (Modern French crête), from Latin crista "tuft, plume," perhaps related to word for "hair" (such as crinis), but it also was used for crest of a cock or a helmet. Replaced Old English hris.
chafer (n.): kind of beetle, Old English ceafor "beetle, cock-chafer," from Proto-Germanic *kabraz- (source also of Old Saxon kevera, Dutch kever, Old High German chevar, German Käfer), literally "gnawer," from PIE *gep(h)- "jaw, mouth" (see jowl (n.1)).
Gallic (adj.): 1670s, "of or pertaining to the French," from Latin Gallicus "pertaining to Gaul or the Gauls," from Latin Gallia "Gaul" and Gallus "a Gaul" from a native Celtic name (see Gaelic), though some connect the word with prehistoric West Germanic *walkhoz "foreigners" (see Welsh). Originally used in English rhetorically or mockingly for "French." The cock as a symbol of France is based on the pun of Gallus "a Gaul" and Latin gallus "cock" (see gallinaceous). Earlier was Gallican (1590s).
It means not simply 'French,' but 'characteristically', 'delightfully', 'distressingly', or 'amusingly' 'French' ... not 'of France', but 'of the typical Frenchman'. [Fowler]
As "of or pertaining to the ancient Gauls" from 1796.
chant (v.): late 14c., from Old French chanter "to sing, celebrate" (12c.), from Latin cantare "to sing," originally frequentative of canere "sing" (which it replaced), from PIE root *kan- "to sing" (source also of Greek eikanos "cock," Old English hana "cock," both literally "bird who sings for sunrise;" Old Irish caniaid "sings," Welsh canu "sing"). The frequentative quality of the word was no longer felt in Latin, and by the time French emerged the word had entirely displaced canere. Related: Chanted; chanting.
claim (v.): c. 1300, "to call, call out; to ask or demand by virtue of right or authority," from accented stem of Old French clamer "to call, name, describe; claim; complain; declare," from Latin clamare "to cry out, shout, proclaim," from PIE *kele- (2) "to shout," imitative (compare Sanskrit usakala "cock," literally "dawn-calling;" Latin calare "to announce solemnly, call out;" Middle Irish cailech "cock;" Greek kalein "to call," kelados "noise," kledon "report, fame;" Old High German halan "to call;" Old English hlowan "to low, make a noise like a cow;" Lithuanian kalba "language"). Related: Claimed; claiming.

Meaning "to maintain as true" is from 1864; specific sense "to make a claim" (on an insurance company) is from 1897. Claim properly should not stray too far from its true meaning of "to demand recognition of a right."