Check nut, Jam nut, Lock nut, a nut which is screwed up tightly against another nut on the same bolt or screw, in order to prevent accidental unscrewing of the first nut. -- Nut buoy. See under Buoy. -- Nut coal, screened coal of a size smaller than stove coal and larger than pea coal; -- called also chestnut coal. - - Nut crab (Zoöl.), any leucosoid crab of the genus Ebalia as, Ebalia tuberosa of Europe. -- Nut grass (Bot.), a plant of the Sedge family (Cyperus rotundus, var. Hydra), which has slender rootstocks bearing small, nutlike tubers, by which the plant multiplies exceedingly, especially in cotton fields. -- Nut lock, a device, as a metal plate bent up at the corners, to prevent a nut from becoming unscrewed, as by jarring. -- Nut pine. (Bot.) See under Pine. -- Nut rush (Bot.), a genus of cyperaceous plants (Scleria) having a hard bony achene. Several species are found in the United States and many more in tropical regions. -- Nut tree, a tree that bears nuts. -- Nut weevil (Zoöl.), any species of weevils of the genus Balaninus and other allied genera, which in the larval state live in nuts.