clam vs hard-shell clam

clam and hard-shell clam both are nouns.

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

As nouns, hard-shell clam is a hyponym of clam; that is, hard-shell clam is a word with a more specific, narrower meaning than clam:

clam: burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness
hard-shell clam: an edible American clam; the heavy shells were used as money by some American Indians

As nouns, hard-shell clam is a hyponym of clam; that is, hard-shell clam is a word with a more specific, narrower meaning than clam:

clam: flesh of either hard-shell or soft-shell clams
hard-shell clam: Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes

Other hyponyms of clam include quahaug, quahog, round clam, long-neck clam, soft-shell clam, steamer, steamer clam.

clam (noun)	hard-shell clam (noun)
burrowing marine mollusk living on sand or mud; the shell closes with viselike firmness	an edible American clam; the heavy shells were used as money by some American Indians
flesh of either hard-shell or soft-shell clams	Atlantic coast round clams with hard shells; large clams usually used for chowders or other clam dishes
a piece of paper money worth one dollar

clam (verb)	hard-shell clam (verb)
gather clams, by digging in the sand by the ocean