The Collaborative International Dictionary of English v.0.48:
clamshell \clamshell\ n. 1. the shell of a clam. [WordNet 1.5] 2. a dredging bucket with hinges like the shell of a clam. Syn: grapple. [WordNet 1.5]WordNet (r) 3.0 (2006):
clamshell n 1: the shell of a clam 2: a dredging bucket with hinges like the shell of a clam [syn: clamshell, grapple]