â¢ CRUSTACEAN (noun). The noun CRUSTACEAN has 1 sense: 1. any mainly aquatic arthropod usually having a segmented body and chitinous exoskeleton. Familiarity information: CRUSTACEAN used as a noun is very rare. â¢ CRUSTACEAN (adjective). The adjective CRUSTACEAN has 1 sense: 1. of or belonging to the class Crustacea. Familiarity information: CRUSTACEAN used as an adjective is very rare.