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