What does "magnesia" mean?

Magnesia: A light earthy white substance, consisting of magnesium oxide, and obtained by heating magnesium hydrate or carbonate, or by burning magnesium. It has a slightly alkaline reaction, and is used in medicine as a mild antacid laxative. See Magnesium. Magnesia alba Etym: [L.] (Med. Chem.), a bulky white amorphous substance, consisting of a hydrous basic carbonate of magnesium, and used as a mild cathartic.