alum
al·um
noun \ˈal-əm\Definition of ALUM
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
