English

Definition of alum noun from the Oxford Advanced Learner's Dictionary

 

alum

 noun
noun
BrE BrE//ˈæləm//
 
; NAmE NAmE//ˈæləm//
 
[uncountable]
 
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a substance formed from aluminium / aluminum and another metal, used, for example, to prepare leather and to change the colour of things Word Origin late Middle English: via Old French from Latin alumen, alumin- related to aluta ‘a kind of leather’.