shellfish

UK: /ˈʃɛlfɪʃ/ US: /ˈʃɛlˌfɪʃ/ ,(shel′fish′)

Inflections of 'shellfish' (n):

shellfish

npl (Especially as a collective plural—e.g. "Some people are allergic to shellfish.")

shellfishes

npl (Mainly used to talk about different types—e.g. "Shellfishes include molluscs and crustaceans.")

WordReference Random House Learner's Dictionary of American English © 2025

shell•fish /ˈʃɛlˌfɪʃ/   n. [countable] , pl. (esp. when thought of as a group) -fish, (esp. for kinds or species) -fish•es. 

1. Invertebrates an animal living in water and having a shell, such as the oyster or other mollusks.

WordReference Random House Unabridged Dictionary of American English © 2025

shell•fish  (shel′fish′), n., pl. (esp. collectively) -fish,  (esp. referring to two or more kinds or species) -fish•es. 

1. Invertebrates an aquatic animal having a shell, as the oyster and other mollusks and the lobster and other crustaceans.

• bef. 900; Middle English; Old English scilfisc. See shell, fish

Collins Concise English Dictionary © HarperCollins Publishers::

shellfish / ˈʃɛlˌfɪʃ/ noun ( -fish, -fishes)

1. any aquatic invertebrate having a shell or shell-like carapace, esp such an animal used as human food. Examples are crustaceans such as crabs and lobsters and molluscs such as oysters