"courage," literally "testicles, balls," 1932, in Hemingway ("Death in the Afternoon," an account of Spanish bull-fighting), from Spanish cojon "testicle," from Latin coleus "the testicles" (source of Italian coglione), literally "strainer bag," a variant of culleus "a leather sack," cognate with Greek koleos "sheath of a sword, scabbard." Both are said in some sources to be from PIE root *kel- (1) "to cover, conceal, save," but de Vaan finds it "Probably a loanword from a non-IE language, independently into Latin and Greek."
English had it as cullion a 16c. term of contempt for a man, "a mean wretch" (Shakespeare) also "a testicle" (Chaucer), from Middle English coujon, coilon (late 14c.), from Old French coillon "testicle; worthless fellow, dolt," from Latin coleus.
1690s, earlier cully (1660s) "a dupe, a sap-head," "a verdant fellow who is easily deceived, tricked, or imposed on" [Century Dictionary], rogues' slang, of uncertain origin.
Perhaps a shortening of cullion "base fellow," originally "testicle" (from French couillon, from Old French coillon "testicle; worthless fellow, dolt," from Latin coleus, literally "strainer bag;" see cojones). Another theory traces it to Romany (Gypsy) chulai "man." Also sometimes in the form cully, however some authorities assert cully was the canting term for "dupe" and cull was generic "man, fellow" without implication of gullibility. Compare also gullible. Related: Cullibility (1728).
Proto-Indo-European root meaning "to cover, conceal, save."
It forms all or part of: Anselm; apocalypse; Brussels; caliology; Calypso; calyx; ceiling; cell; cellar; cellular; cellulite; cellulitis; cilia; clandestine; cojones; coleoptera; color; conceal; eucalyptus; hall; hell; helm (n.2) "a helmet;" helmet; hold (n.2) "space in a ship below the lower deck;" hole; hollow; holster; housing (n.2) "ornamental covering;" hull (n.1) "seed covering;" kil-; kleptomania; occult; rathskeller; supercilious; Valhalla; William.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit cala "hut, house, hall;" Greek kalia "hut, nest," kalyptein "to cover," koleon, koleos "sheath," kelyphos "shell, husk;" Latin cella "small room, store room, hut," celare "to hide, conceal," clam "secret," clepere "to steal, listen secretly to;" Old Irish cuile "cellar," celim "hide," Middle Irish cul "defense, shelter;" Gothic hulistr "covering," Old English heolstor "lurking-hole, cave, covering," Gothic huljan "to cover over," hulundi "hole," hilms "helmet," halja "hell," Old English hol "cave," holu "husk, pod;" Old Prussian au-klipts "hidden;" Old Church Slavonic poklopu "cover, wrapping."
