Main Entry: al·um

Pronunciation: \ˈal-əm\

Function: noun

1 : either of two colorless or white crystalline double sulfates of aluminum used in medicine internally as emetics and locally as astringents and styptics: a : one KAl(SO₄)₂·12H₂O that is a sulfate of aluminum and potassium—called also potassium alum b : one consisting of an ammonium aluminum sulfate NH₄Al(SO₄)₂·12H₂O—called also ammonia alum, ammonium alum
2 : any of various double salts isomorphous with potassium aluminum sulfate