lake duck vs Aythya affinis

lake duck and Aythya affinis both are nouns.

Word	Noun	Adjective	Verb	Adverb
lake duck	Yes	No	No	No
Aythya affinis	Yes	No	No	No

As nouns, lake duck and Aythya affinis are synonyms defined as:

lake duck and Aythya affinis: common scaup of North America; males have purplish heads

Other synonyms of lake duck include lesser scaup, lesser scaup duck.

lake duck (noun)	Aythya affinis (noun)
common scaup of North America; males have purplish heads	common scaup of North America; males have purplish heads