alum

(noun) a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum. Synonyms: ammonia alum, ammonium alum.

(noun) a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum. Synonyms: potassium alum, potash alum.

(noun) a person who has received a degree from a school (high school or college or university). Synonyms: alumnus, alumna, graduate, grad.

(noun) a double sulphate of aluminum and potassium that is used as an astringent (among other things).