definition of
alum

[1] #1 alum n. [ammonia alum, ammonium alum] a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum. wn

[2] #2 alum n. [potassium alum, potash alum] a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum. wn

[3] #3 alum n. [alumnus, alumna, graduate, grad] a person who has received a degree from a school (high school or college or university). wn

[4] #4 alum n. a double sulphate of aluminum and potassium that is used as an astringent (among other things). wn