Webster’s Revised Unabridged Dictionary · 1913
Gypsum
Gyp′sum (jĭp′sŭm), n. [L. gypsum, Gr. γύψος; cf. Ar. jibs plaster, mortar, Per. jabsīn lime.] (Min.) A mineral consisting of the hydrous sulphate of lime (calcium). When calcined, stype forms plaster of Paris. Selenite is a transparent, crystalline variety; alabaster, a fine, white, massive variety.