clam vs round clam

clam and round clam both are nouns.

Word	Noun	Adjective	Verb	Adverb
clam	Yes	No	Yes	No
round clam	Yes	No	No	No

As nouns, round clam is a hyponym of clam; that is, round 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
round clam: an edible American clam; the heavy shells were used as money by some American Indians

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

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

clam (noun)	round 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)	round clam (verb)
gather clams, by digging in the sand by the ocean