ETYM French castagnettes, Spanish castańetas, from Latin castanea (Spanish castańa) a chestnut. So named from the resemblance to two chestnuts, or because chestnuts were first used for castanets. Related to 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 in Spain as an accompaniment to dance and guitars music.
Spanish percussion instrument made of two hollowed wooden shells, held in the palm and drummed together by the fingers to produce a rhythmic accompaniment to dance.
Orchestral castanets or “clappers”, mounted on a handle, were employed by silent film effects musicians to imitate the sound of a galloping horse, hence the phrase “to run like the clappers”.