waterfowl, natatorial bird of the family Anatidae, Old English duce (found only in genitive ducan) "a duck," literally "a ducker," presumed to be from Old English *ducan "to duck, dive" (see duck (v.)). Replaced Old English ened as the name for the bird, this being from PIE *aneti-, the root of the "duck" noun in most Indo-European languages.

In the domestic state the females greatly exceed in number, hence duck serves at once as the name of the female and of the race, drake being a specific term of sex. [OED]

As a term of endearment, attested from 1580s (see ducky). duck-walk, a squatting waddle done by a person, in imitation of a duck, is by 1915; duck soup, slang for "anything easily done," is by 1899. Duck's ass haircut is from 1951. Ducks-and-drakes, skipping flat stones on water, is from 1580s; the figurative sense of "throwing something away recklessly" is c. 1600.