jackknife clam vs knife-handle

jackknife clam and knife-handle both are nouns.

Word	Noun	Adjective	Verb	Adverb
jackknife clam	Yes	No	No	No
knife-handle	Yes	No	No	No

As nouns, jackknife clam and knife-handle are synonyms defined as:

jackknife clam and knife-handle: marine clam having a long narrow curved thin shell

Other synonyms of jackknife clam include razor clam.

jackknife clam (noun)	knife-handle (noun)
marine clam having a long narrow curved thin shell	marine clam having a long narrow curved thin shell