Giant clam Meaning, Definition & Usage

  1. noun a large clam inhabiting reefs in the southern Pacific and weighing up to 500 pounds
    Tridacna gigas.

WordNet

Definitions
  1. (Zoöl.), a bivalve shell of the genus Tridacna, esp. T. gigas, which sometimes weighs 500 pounds. The shells are sometimes used in churches to contain holy water.

Webster 1913