alum

باللغة العربية: شَبّ

1. An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and aluminium (K₂SO₄·Al₂(SO₄)₃·24H₂O). (countable, uncountable)
2. Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations. (countable, uncountable)

الجمع alums