American Heritage Dictionary of the English Language, 5th Edition
Origin uncertain. Perhaps Old English cokeren; compare Welshcocru (“to indulge, fondle”), Frenchcoqueliner (“to dandle, to imitate the crow of a cock, to run after the girls”), and Englishcockle and cock (“a bird”).
From Middle English coker "a quiver, boot" from Old English cocer "quiver, case" from Proto-Germanic*kukur- (“container, case”). More at quiver.