Main Entry: ¹al·um

Pronunciation: \ˈa-ləm\

Function: noun

Etymology: Middle English, from Anglo-French alum, alun, from Latin alumen

Date: 14th century

1 : a potassium aluminum sulfate KAl(SO₄)₂·12H₂O or an ammonium aluminum sulfate NH₄Al(SO₄)₂·12H₂O used especially as an emetic and as an astringent and styptic
2 : any of various double salts isomorphous with potassium aluminum sulfate
3 : aluminum sulfate