(mag·nē′zhə, -shə, -zē·ə) noun Chem.
Magnesium oxide, MgO, a light, white, earthy powder, used in medicine as an antacid laxative, in glassmaking, etc. It can be made by burning magnesium or by igniting certain of the magnesium salts.
—milk of magnesia A milk–white aqueous suspension of magnesium hydroxide, Mg(OH)₂: used as a laxative and antacid. [<Med. L <Gk. Magnēsia (lithos) (stone) of Magnesia <Magnēsia Magnesia (def. 2)]
—mag·ne′sian, mag·ne′sic adjective

(mag·nē′zhə, -shə)
1. An ancient city of Lydia, western Asia Minor, on the site of modern Manissa; scene of the defeat of Antiochus the Great by the two Scipios, 190 B.C. Also Magnesia ad Si·py·lum (ad sip′ə·lum).
2. In classical geography, the coastal district of Thessaly south of the Vale of Tempe, part of which forms a nome of modern Greece.