alum

noun

1. 1

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

2. 2

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

3. 3

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

4. 4

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