hard-shell clam vs hard clam

hard-shell clam and hard clam both are nouns.

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

As nouns, hard-shell clam and hard clam are synonyms defined as:

hard-shell clam and hard clam: an edible American clam; the heavy shells were used as money by some American Indians

Other synonyms of hard-shell clam include Mercenaria mercenaria, quahaug, quahog, round clam, Venus mercenaria.

hard-shell clam (noun)	hard clam (noun)
an edible American clam; the heavy shells were used as money by some American Indians	an edible American clam; the heavy shells were used as money by some American Indians
Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes