| Noun | 1. | gypsum - a common white or colorless mineral (hydrated calcium sulphate) used to make cements and plasters (especially plaster of Paris)atomic number 20, Ca, calcium - a white metallic element that burns with a brilliant light; the fifth most abundant element in the earth's crust; an important component of most plants and animals mineral - solid homogeneous inorganic substances occurring in nature having a definite chemical composition alabaster - a compact fine-textured, usually white gypsum used for carving gesso - gypsum or plaster of Paris spread on a surface to make it suitable for painting or gilding (or a surface so prepared) terra alba - finely pulverized gypsum used especially as a pigment calcium sulfate, calcium sulphate - a white salt (CaSO4) plaster of Paris, plaster - any of several gypsum cements; a white powder (a form of calcium sulphate) that forms a paste when mixed with water and hardens into a solid; used in making molds and sculptures and casts for broken limbs |