Etymology
cuckold (n.)

derisive name for a man whose wife is false to him, "husband of an adulteress," early 13c., kukewald, cokewold, from Old French cucuault, from cocu (see cuckoo) + pejorative suffix -ault, of Germanic origin. So called from the female bird's alleged habit of changing mates, or her authentic habit of leaving eggs in another bird's nest.

In Modern French the identity is more obvious: Coucou for the bird and cocu for the betrayed husband. German Hahnrei (13c.), from Low German, is of obscure origin. The second element seems to be connected to words for "ardent," and suggests perhaps "sexually aggressive hen," with transferal to humans, but Kluge suggests rather a connection to words for "capon" and "castrated." The female equivalent, cuckquean, is attested by 1560s.

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cuckold (v.)

of a wife or her paramour, "to dishonor (a husband) by adultery," 1580s, from cuckold (n.). Related: Cuckolded; cuckolding.

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cuckoldry (n.)

1520s, "adultery as affecting the honor of the husband," from cuckold (n.) + -ery.

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wittol (n.)
"compliant cuckold," late 15c., witewold, probably from witen "to know" (see wit (v.)) + ending from noun cuckold (Middle English cokewold).
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Actaeon 
in Greek mythology, the name of the hunter who discovered Artemis bathing and was changed by her to a stag and torn to death by his hounds. The name is of unknown origin. Sometimes used figuratively in 17c. for "a cuckold" (because of his "horns").
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forked (adj.)

c. 1300, "branched or divided in two parts," past-participle adjective from fork (v.). Of roads from 1520s; from 1550s as "pointing more than one way." In 16c.-17c. sometimes with a suggestion of "cuckold," on the notion of "horned." Forked tongue as a figure of duplicitous speech is from 1885, American English. Double tongue in the same sense is from 15c.

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horn (v.)
1690s, "to furnish with horns," from horn (n.). Earlier in figurative sense of "to cuckold" (1540s). Meaning "to push with the horns" (of cattle, buffalo, etc.) is from 1851, American English; phrase horn in "intrude" is by 1880, American English, originally cowboy slang. Related: Horned; horning.
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shoehorn (v.)

1859, "put or thrust (something somewhere) by means of a 'tool,' " a figurative use, from shoehorn (n.). By 1927 as "maneuver or compress (someone or something) into inadequate space." Earlier it meant "to cuckold" (mid-17c.), with a play on horn (n.). Related: Shoehorned; shoehorning.

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cuckoo (n.)

European bird noted for its love-note cry and notorious for parasitism, c. 1300, cokkou (late 12c. as a surname), from Old French cocu "cuckoo," also "cuckold," echoic of the male bird's mating cry (compare Greek kokkyx, Latin cuculus, Middle Irish cuach, Sanskrit kokilas).

Slang adjectival sense of "crazy" is American English, 1918, but noun meaning "stupid person" is recorded by 1580s, perhaps from the bird's unvarying, oft-repeated call. The Old English name was ʒeac, cognate with Old Norse gaukr, source of Scottish and northern English gowk, which also has insulting senses. The Germanic words presumably originally were echoic, too, but had drifted in form. Cuckoo-clock is from 1789.

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