sawbill vs fish duck

sawbill and fish duck both are nouns.

Word	Noun	Adjective	Verb	Adverb
sawbill	Yes	No	No	No
fish duck	Yes	No	No	No

As nouns, sawbill and fish duck are synonyms defined as:

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

Other synonyms of sawbill include merganser, sheldrake.

sawbill (noun)	fish duck (noun)
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