Frustum Frus"tum, n.; pl. L. Frusta, E. Frustums. [L. fruslum piece, bit.] 1. (Geom.) The part of a solid next the base, formed by cutting off the, top; or the part of any solid, as of a cone, pyramid, etc., between two planes, which may be either parallel or inclined to each other. 2. (Arch.) One of the drums of the shaft of a column.