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alum1

Syllabification: (a·lum)

Pronunciation: /ˈaləm/

Definition of alum

noun

Chemistry

a colorless astringent compound that is a hydrated double sulfate of aluminum and potassium, used in solution medicinally and in dyeing and tanning. Also called potash alum.
- Chemical formula: AlK(SO₄)₂.12H₂O
any of a number of analogous crystalline double sulfates of a monovalent metal (or group) and a trivalent metal.