a white powder that sets to a hard solid when mixed with water, used for making sculptures and casts, as an additive for lime plasters, and for making casts for setting broken limbs. It is usually the hemihydrate of calcium sulphate, 2CaSO4.H2O
2.
the hard plaster produced when this powder is mixed with water: a fully hydrated form of calcium sulphate
Sometimes shortened to: plaster
Word origin
C15: from Medieval Latin plastrum parisiense, originally made from the gypsum of Paris