plaster of paris
- noun (written as plaster of Paris)a white powder, calcium sulfate, that forms a rapidly hardening paste when mixed with water and is used in sculpture, plaster casts for broken limbs, and in the collection of delicate fossils
- gypsum, from which three-quarters of the chemically bound water has been driven off by heating. When wetted, it recombines with water and hardens quickly. See also hemihydrate.