hard-shell clam vs genus Venus

hard-shell clam and genus Venus both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard-shell clam	Yes	No	No	No
genus Venus	Yes	No	No	No

hard-shell clam (noun)	genus Venus (noun)
an edible American clam; the heavy shells were used as money by some American Indians	type genus of the family Veneridae: genus of edible clams with thick oval shells
Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes