razor clam vs jackknife clam

razor clam and jackknife clam both are nouns.

Word	Noun	Adjective	Verb	Adverb
razor clam	Yes	No	No	No
jackknife clam	Yes	No	No	No

As nouns, razor clam and jackknife clam are synonyms defined as:

razor clam and jackknife clam: marine clam having a long narrow curved thin shell

Other synonyms of razor clam include knife-handle.

razor clam (noun)	jackknife clam (noun)
marine clam having a long narrow curved thin shell	marine clam having a long narrow curved thin shell