clam

Concise Oxford English Dictionary © 2008 Oxford University Press:
clam/klam/

▶noun

• 1 a large marine bivalve mollusc with shells of equal size, several kinds of which are edible. [Mya arenaria (softshell clam), Venus mercenaria (hardshell clam, both N. America), Tridacna gigas (giant clam, Indo-Pacific), and many other species.]

• 2 US informal a dollar.

▶verb (clams, clamming, clammed)

• 1 chiefly N. Amer. dig for or collect clams.

• 2 (clam up) informal abruptly stop talking.

– origin C16: appar. from earlier clam ‘a clamp’, from OE clam, clamm ‘a bond or bondage’, of Gmc origin; rel. to clamp1; sense 2 of the noun is of unknown origin.