merganser

n. [ Sp. mergánsar, fr. mergo a diver (L. mergus, fr. mergere to dip, dive) + ánsar goose, L. anser. ] (Zool.) Any bird of the genus Mergus (Merganser), and allied genera of the subfamily Merginae. They are allied to the ducks, but have a sharply serrated bill, eat fish, and dive for food. Also called fish duck. [ 1913 Webster +PJC ]

☞ The red-breasted merganser (Merganser serrator) inhabits both hemispheres. It is called also sawbill, harle, and sheldrake. The American merganser (Merganser Americanus.) and the hooded merganser (Lophodytes cucullatus) are well-known species. --
White merganser, the smew or white nun. [ 1913 Webster ]