What word does your mother always say?
magnesium sulphate, 1770, obtained from Epsom water, the water of a mineral spring at Epsom in Surrey, England, the medicinal properties of which were discovered in Elizabethan times. The place name is recorded c.973 as Ebbesham, literally "Ebbi's homestead," from the name of some forgotten Anglo-Saxon. The mineral supply there was exhausted 19c.
Epsom salts Ep·som salts (ěp'səm)
Hydrated magnesium sulfate, used as a cathartic and as an agent to reduce inflammation.