merganser vs sheldrake

merganser and sheldrake both are nouns.

Word	Noun	Adjective	Verb	Adverb
merganser	Yes	No	No	No
sheldrake	Yes	No	No	No

As nouns, merganser and sheldrake are synonyms defined as:

merganser and sheldrake: large crested fish-eating diving duck having a slender hooked bill with serrated edges

Other synonyms of merganser include fish duck, sawbill.

merganser (noun)	sheldrake (noun)
large crested fish-eating diving duck having a slender hooked bill with serrated edges	Old World gooselike duck slightly larger than a mallard with variegated mostly black-and-white plumage and a red bill
	large crested fish-eating diving duck having a slender hooked bill with serrated edges