Calomel /(kăl"ō̇*mĕl)/

Cal·o·mel

Calomel

n.
  1. 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. (Chem.)