Definition of alum
(Entry 1 of 3)
1 : a potassium aluminum sulfate KAl(SO4)2·12H2O or an ammonium aluminum sulfate NH4Al(SO4)2·12H2O used especially for its astringent and styptic properties
2 : any of various double salts isomorphous with potassium aluminum sulfate
3 : aluminum sulfate
alum
noun (2)alum
abbreviationDefinition of alum (Entry 3 of 3)
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Time Traveler for alum
The first known use of alum was in the 14th century
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