scaup vs greater scaup

scaup and greater scaup both are nouns.

Word	Noun	Adjective	Verb	Adverb
scaup	Yes	No	No	No
greater scaup	Yes	No	No	No

As nouns, greater scaup is a hyponym of scaup; that is, greater scaup is a word with a more specific, narrower meaning than scaup:

scaup: diving ducks of North America having a bluish-grey bill
greater scaup: large scaup of North America having a greenish iridescence on the head of the male

Other hyponyms of scaup include Aythya marila, Aythya affinis, lake duck, lesser scaup, lesser scaup duck.

scaup (noun)	greater scaup (noun)
diving ducks of North America having a bluish-grey bill	large scaup of North America having a greenish iridescence on the head of the male