a white substance, calcium oxide, CaO, obtained by the action of heat on limestone, shells, and other material containing calcium carbonate, and used in making mortar and cement, and, when hydrated, in neutralizing acid soil
a calcareous deposit from water inside pipes, pans, etc.
b. Any of various mineral and industrial forms of calcium oxide differing chiefly in water content and percentage of constituents such as silica, alumina, and iron. Also called quicklime.