'Shellfish' definitions:

Definition of 'shellfish'

From: WordNet
noun
Meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)
noun
Invertebrate having a soft unsegmented body usually enclosed in a shell [syn: mollusk, mollusc, shellfish]

Definition of 'Shellfish'

From: GCIDE
  • Shellfish \Shell"fish`\, n. (Zool.) Any aquatic animal whose external covering consists of a shell, either testaceous, as in oysters, clams, and other mollusks, or crustaceous, as in lobsters and crabs. [1913 Webster]