merganser
Concise Oxford English Dictionary © 2008 Oxford University Press:
merganser /məːˈganzə, -sə/
▶noun a fish-eating diving duck with a long, thin serrated and hooked bill. [Mergus serrator (red-breasted merganser) and related species.]
– origin C17: mod. L., from L. mergus ‘diver’ + anser ‘goose’.
'merganser' also found in these Oxford entries:

