E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Coward (anciently written culvard)
is either from the French, couard, originally written culvert, from culver (a pigeon), pigeon-livered being still a common expression for a coward; or else from the Latin, culum vertere, to turn tail (Spanish, cobarde; Portuguese, covarde; Italian, codardo, a coward, Latin, cauda, a tail). A beast cowarded, in heraldry, is one drawn with its coue or tail between its legs. The allusion is to the practice of beasts, who sneak off in this manner when they are cowed.