sheldrake vs merganser

sheldrake and merganser both are nouns.

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

As nouns, sheldrake and merganser are synonyms defined as:

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

Other synonyms of sheldrake include fish duck, sawbill.

sheldrake (noun)	merganser (noun)
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
large crested fish-eating diving duck having a slender hooked bill with serrated edges