Small, hand-held instrument made of concave shells of ivory or hard wood used by Spanish dancers to accompany dances such as the bolero, cachucha, etc. with a sharp clapping sound.a percussion instrument, consisting of two hollowed-out wooden shells, which are played by clicking them together with the fingers. used by Spanish dancers. When used in an orchestra, castanets are usually mounted on a small stick to they can be shaken together more easily<br><br>Or bones. A pair of wooden instruments that are held in the hand (between the thumb and forefinger) and are clicked together in rhythm.