American merganser vs sawbill

American merganser and sawbill both are nouns.

Word	Noun	Adjective	Verb	Adverb
American merganser	Yes	No	No	No
sawbill	Yes	No	No	No

As nouns, sawbill is a hypernym of American merganser; that is, sawbill is a word with a broader meaning than American merganser:

American merganser: common North American diving duck considered a variety of the European goosander
sawbill: large crested fish-eating diving duck having a slender hooked bill with serrated edges

Other hypernyms of American merganser include fish duck, merganser, sheldrake.

American merganser (noun)	sawbill (noun)
common North American diving duck considered a variety of the European goosander	large crested fish-eating diving duck having a slender hooked bill with serrated edges