fish duck vs sawbill

fish duck and sawbill both are nouns.

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

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

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

Other synonyms of fish duck include merganser, sheldrake.

fish duck (noun)	sawbill (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