BARREL, 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). It is a word of uncertain origin com mon to Romance languages. The term barrel is applied to many cylindrical objects, e.g., 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 music-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.