calomel

n. [ Gr. kalo`s beautiful + me`las black. So called from its being white, though made from a black mixture of mercury and corrosive sublimate. Cf. F. calomélas. ] (Chem.) Mild chloride of mercury, Hg2Cl2, a heavy, white or yellowish white substance, insoluble and tasteless, much used in medicine as a mercurial and purgative; mercurous chloride. It occurs native as the mineral horn quicksilver. [ 1913 Webster ]