Cas"ta*nets, 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.

&fist; The singular, castanet, is used of one of the pair, or, sometimes, of the pair forming the instrument.

The dancer, holding a castanet in each hand, rattles then to the motion of his feet.
Moore (Encyc. of Music).

• percussion instrument (idiophone) consisting of a pair of concave shells joined on one edge by string, held in the hand and used to produce clicking sounds