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Related to clam up: clammer, Long clam
a. Any of various usually burrowing marine and freshwater bivalve mollusks chiefly of the subclass Heterodonta, including members of the families Veneridae and Myidae, many of which are edible.
b. The soft edible body of such a mollusk.
2. Informal A close-mouthed person, especially one who can keep a secret.
3. Slang A dollar: owed them 75 clams.
intr.v. clammed, clam·ming, clamsPhrasal Verb:
To hunt for clams.
clam up Informal
To refuse to talk.
[From obsolete clam-shell, shell that clamps, clam, from clam.]
A clamp or vise.
[Middle English, from Old English clam, clamm, bond, fetter.]
(intr, adverb) informal to keep or become silent or withhold information