Is it ensure, insure, or assure?
A drum consisting of a skin stretched over a large shell in the shape of a half-sphere. The pitch of the kettledrum can be changed by manipulating screws at the edge of the skin or pedals at the bottom of the drum. Kettledrums are usually used in classical music in sets of two or more and are known by their Italian name, timpani.
percussion instrument in which a membrane is stretched over a hemispheric or similar-shaped shell and held taut, usually by a hoop with rope lacings, adjusting screws, or various mechanical devices; in some varieties the lacings may pierce the skin directly or the membrane may be tied on with a thong. When struck by sticks or, less commonly, by the hands, the membrane produces a sound of identifiable pitch. The form of the sound wave is not completely known, nor are the acoustic roles of the shell's shape and the volume of air it encloses.