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

2. a person who has received a degree from a school (high school or college or university)

Synonym: alumnusalumnagraduategrad

3. a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum

Synonym: potassium alumpotash alum

4. a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum

Synonym: ammonia alumammonium alum