crab vs soft-shell crab

crab and soft-shell crab both are nouns.

Word	Noun	Adjective	Verb	Adverb
crab	Yes	No	Yes	No
soft-shell crab	Yes	No	No	No

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

crab: decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers
soft-shell crab: edible crab that has recently molted and not yet formed its new shell

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

crab: the edible flesh of any of various crabs
soft-shell crab: freshly molted crab with new shell still tender and flexible

crab (noun)	soft-shell crab (noun)
a stroke of the oar that either misses the water or digs too deeply	edible crab that has recently molted and not yet formed its new shell
decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers	freshly molted crab with new shell still tender and flexible
a louse that infests the pubic region of the human body
the edible flesh of any of various crabs
a quarrelsome grouch

crab (verb)	soft-shell crab (verb)
complain
fish for crab
scurry sideways like a crab
direct (an aircraft) into a crosswind