alum Meaning, Definition & Usage

noun a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum
ammonia alum; ammonium alum.
noun a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum
potash alum; potassium alum.
noun a person who has received a degree from a school (high school or college or university)
alumna; grad; alumnus; graduate.
noun a double sulphate of aluminum and potassium that is used as an astringent (among other things)

OE. alum, alom, OF. alum, F. alun, fr. L. alumen alum.

(Chem.) A double sulphate formed of aluminium and some other element (esp. an alkali metal) or of aluminium. It has twenty-four molecules of water of crystallization. ✍ Common alum is the double sulphate of aluminium and potassium. It is white, transparent, very astringent, and crystallizes easily in octahedrons. The term is extended so as to include other double sulphates similar to alum in formula.

To steep in, or otherwise impregnate with, a solution of alum; to treat with alum. Ure.