Often, Epsom salts . Chem., Pharm. 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.
[ 1760-70; after EPSOM; so called from its presence in the local mineral water ]