n. A piece; particularly, a remaining piece of something of which a part is lacking, as the drum of a column.n. In geometry, the part of a solid next the base, left after cutting off the top part by a plane parallel to the base; or the part of any solid between two planes, which may be either parallel or inclined to each other: as, the frustum of a cone, of a pyramid, of a conoid, of a spheroid, or of a sphere.