Barrel (a word of uncertain origin common to Romance languages; the Celtic forms, as in the Gaelic baraill, are derived from the English), a vessel of cylindrical shape, made of staves bound together by hoops, a cask; also a dry and liquid measure of capacity, varying with the commodity which it contains (see Weights and Measures). The term is applied to many cylindrical objects, as to the drum round which the chain is wound in a crane, a capstan or a watch; to the cylinder studded with pins in a barrel-organ or musical-box; to the hollow shaft in which the piston of a pump works; or to the tube of a gun. The "barrel" of a horse is that part of the body lying between the shoulders and the quarters. For the system of vaulting in architecture known as "barrel-vaulting" see Vault.