%castanet%

n. pl. [ F. castagnettes, Sp. castañetas, fr. L. castanea (Sp. castaña) a chestnut. So named from the resemblance to two chestnuts, or because chestnuts were first used for castanets. See Chestnut. ] Two small, concave shells of ivory or hard wood, shaped like spoons, fastened to the thumb, and beaten together with the middle finger; -- used by the Spaniards and Moors as an accompaniment to their dance and guitars. [ 1913 Webster ]

☞ The singular, castanet, is used of one of the pair, or, sometimes, of the pair forming the instrument. [ 1913 Webster ]

The dancer, holding a castanet in each hand, rattles them to the motion of his feet. Moore (Encyc. of Music). [ 1913 Webster ]