Definition of alums:
(n) :
(Canada, US) A past attendee or graduate (of any gender) of a college, university or other educational institution.
(n) :
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).
(n) :
(inorganic chemistry) 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.
(v) :
(transitive) To steep in, or otherwise impregnate with, a solution of alum; to treat with alum.