"one who lacks courage to meet danger or shrinks from the chance of being hurt," mid-13c., from Anglo-French couard, couart, 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" (see coda) + -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 (Old Spanish couarde) are from French. The spelling in English was influenced by cow (v. and n.).
[S]o strong is the false belief that every bully must be a coward that acts requiring great courage are constantly described as cowardly or dastardly if they are so carried out as not to give the victim a sporting chance; the throwing of a bomb at a king's carriage is much less dastardly than shooting a partridge, because the thrower takes a very real risk .... [Fowler]
As a surname (attested from mid-13c.) it represents Old English cuhyrde "cow-herd." As an adjective, "lacking courage, timorous," from late 13c. Farmer has coward's castle "a pulpit," "Because a clergyman may deliver himself therefrom without fear of contradiction or argument."