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late 13c., agent noun from clap (v.). Meaning "tongue of a bell" is from late 14c. Old English had clipur. Meaning "hinged board snapped in front of a camera at the start of filming to synchronize picture and sound" is from 1940.
musicalmusical instrument consisting of pieces of wood, bone, metal, or other sonorous substance either held in both hands or, fastened together, held in one hand, sometimes with a handle, and struck against each other. Clappers have been played throughout the world since ancient times, often with a ritual, warning, work-coordinating, or signaling function, rather than a musical one.