Real Dictionary

castanets
Castanets are a Spanish musical instrument consisting of two small round pieces of wood or plastic held together by a cord. You hold the castanets in your hand and knock the pieces together with your fingers.

castanets in American English
a pair of small, hollowed pieces of hard wood, ivory, etc., held in the hand by a connecting cord and clicked together with the fingers to beat time to music, esp. in Spanish dances

castanets in British English
plural noun: curved pieces of hollow wood, usually held between the fingers and thumb and made to click together: used esp by Spanish dancers