lamellibranch(noun, adjective) adjective1. bivalveSimilar word(s): bivalve, bivalved, pelecypod, pelecypodous noun1. marine or freshwater mollusks having a soft body with platelike gills enclosed within two shells hinged togetherSimilar word(s): bivalve, pelecypodDefinition categories: animal, mollusc, mollusk, shellfish