crawdad vs shellfish

crawdad and shellfish both are nouns.

Word	Noun	Adjective	Verb	Adverb
crawdad	Yes	No	No	No
shellfish	Yes	No	No	No

As nouns, shellfish is a hypernym of crawdad; that is, shellfish is a word with a broader meaning than crawdad:

crawdad: tiny lobster-like crustaceans usually boiled briefly
shellfish: meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)

crawdad (noun)	shellfish (noun)
small freshwater decapod crustacean that resembles a lobster	invertebrate having a soft unsegmented body usually enclosed in a shell
tiny lobster-like crustaceans usually boiled briefly	meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)