mussel

Concise Oxford English Dictionary © 2008 Oxford University Press:
mussel/ˈmʌsl/

▶noun

• 1 a marine bivalve mollusc with a dark brown or purplish-black shell. [Mytilus edulis (edible mussel) and other species, family Mytilidae.]

• 2 a freshwater bivalve mollusc, some kinds of which produce small pearls. [Family Unionidae.]

– origin OE mus(c)le; ult. from late L. muscula, from L. musculus (see muscle).