Hard-shelled mollusks that live in water and can be eaten, or a person's mouth when told to stay quiet (slang).
From Old English 'clam' possibly related to 'clamp,' referring to the shell's clamping action. The seafood meaning is primary, while the slang 'shut your clams' (meaning be quiet) emerged from comparing lips to a shell.
Clams are one of the most ancient foods humans ate—shell middens (ancient trash heaps) show people were eating clams over 150,000 years ago! They're also filter feeders that help clean ocean water, making them both food and environmental helpers.
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