noun

1. magnesium oxide, MgO, a white, tasteless powder, used as a mild laxative and antacid, and as an insulating substance, in firebrick, etc.
2. hydrated magnesium carbonate, also used as a laxative

Etymology: ModL magnesia (alba), lit., (white) magnesia (in contrast to ML magnesia, a black mineral < LGr magnēsia < Magnēsia, Magnesia): term substituted by F. Hoffmann (1660-1742), Ger physician, for ModL magnes carneus, lit., flesh-magnet (see magnet & carnal): so named from clinging to the lips