Epsom salt

noun

1. Chemistry, Pharmacology.,  Often Epsom salts. hydrated magnesium sulfate, MgSO 4 ⋅7H 2 O, occurring as small colorless crystals: used in fertilizers, the dyeing of fabrics, leather tanning, etc., and in medicine chiefly as a cathartic.

Word History and Origins

Origin of Epsom salt¹

1760–70; after Epsom; so called from its presence in the local mineral water