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English definition of “alum”

alum

noun [U]     /ˈæl.əm/ specialized
a chemical substance containing aluminium used in dyeing (= changing the colour of something) and as an astringent (= substance that causes skin to tighten)Specific chemicals, chemical compounds and gasesSubstances and structures in the bodyTypes of chemical
(Definition of alum noun from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
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