cal·o·mel 
(kălə-mĕl′, -məl)
(kălə-mĕl′, -məl)n.
A white or brown tasteless powder, Hg2Cl2, used as an insecticide and formerly as a purgative. Also called mercurous chloride.
[Probably from New Latin calomelās : Greek kalos, beautiful + melās, black.]