"alum" in the noun sense
1. alum, ammonia alum, ammonium alum
a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum
2. alum, potassium alum, potash alum
a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum
3. alumnus, alumna, alum, graduate, grad
a person who has received a degree from a school (high school or college or university)
a double sulphate of aluminum and potassium that is used as an astringent (among other things)
Source: WordNet® (An amazing lexical database of English)
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