French, literally "a great heap" (13c.), from beau "fine, great" (see beau (n.)) + coup "a stroke," also "a throw," hence, "a heap" (see coup (n.)). Compare Spanish golpe "multitude," from the same Latin source.
"attendant suitor of a lady," 1720, from French beau "the beautiful," noun use of an adjective, from Old French bel "beautiful, handsome, fair, genuine, real" (11c.), from Latin bellus "handsome, fine, pretty, agreeable" (see belle). Meaning "man who attends excessively to dress, etiquette, etc.; a fop; a dandy" is from 1680s, short for French beau garçon "pretty boy" (1660s). Plural is beaus or beaux. Beau Brummel, arbiter of men's fashion in Regency London, was George B. Brummel, gentleman (1778-1840).
c. 1400, "a blow" (obsolete), from Old French coup, colp "a blow, strike" (12c.), from Medieval Latin colpus, from Vulgar Latin *colapus, from Latin colaphus "a cuff, box on the ear," from Greek kolaphos "a blow, buffet, punch, slap," "a lowly word without clear etymology" [Beekes].
Meaning "a sudden decisive act" is 1852, short for coup d'etat. In Modern French the word is a workhorse, describing everything from a pat on the back to a whipping, and is used as well of thunder, gusts of wind, gunshots, and chess moves.