goosander vs fish duck

goosander and fish duck both are nouns.

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

As nouns, fish duck is a hypernym of goosander; that is, fish duck is a word with a broader meaning than goosander:

goosander: common merganser of Europe and North America
fish duck: large crested fish-eating diving duck having a slender hooked bill with serrated edges

Other hypernyms of goosander include merganser, sawbill, sheldrake.

goosander (noun)	fish duck (noun)
common merganser of Europe and North America	large crested fish-eating diving duck having a slender hooked bill with serrated edges