mid-13c., from Old French coart "coward" (no longer the usual word in French, which has now in this sense poltron, from Italian, and lâche), from coe "tail," from Latin coda, popular dialect variant of cauda "tail," of uncertain origin + -ard, an agent noun suffix denoting one that carries on some action or possesses some quality, with derogatory connotation (see -ard).
The word probably reflects an animal metaphoric sense still found in expressions like turning tail and tail between legs. Coart was the name of the hare in Old French versions of "Reynard the Fox." Italian codardo, Spanish cobarde are from French.
The identification of coward & bully has gone so far in the popular consciousness that persons & acts in which no trace of fear is to be found are often called coward(ly) merely because advantage has been taken of superior strength or position .... [Fowler]As a surname (attested from 1255) it represents Old English cuhyrde "cow-herd." Farmer has coward's castle "a pulpit," "Because a clergyman may deliver himself therefrom without fear of contradiction or argument."