Aythya affinis vs lake duck

Aythya affinis and lake duck both are nouns.

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

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

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

Other synonyms of Aythya affinis include lesser scaup, lesser scaup duck.

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