crustacean vs arthropod

crustacean and arthropod both are nouns.

Word	Noun	Adjective	Verb	Adverb
crustacean	Yes	Yes	No	No
arthropod	Yes	No	No	No

As nouns, arthropod is a hypernym of crustacean; that is, arthropod is a word with a broader meaning than crustacean:

crustacean: any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton
arthropod: invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin

crustacean (noun)	arthropod (noun)
any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton	invertebrate having jointed limbs and a segmented body with an exoskeleton made of chitin

crustacean (adjective)	arthropod (adjective)
of or belonging to the class Crustacea