Calomel

noun

1. A white or brown tasteless powder, Hg2Cl2, used as an insecticide and formerly as a purgative.
2. Hemi-, sub-, or protochlorid of mercury, or mercurous chlorid, Hg2Cl2.
3. 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.
4. mercurous chloride Hg2Cl2
5. a tasteless colorless powder used medicinally as a cathartic