Meaning

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

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

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

originClipping of alumnus and alumna (> alumn- > alum), by the removal of the originally Latin gender-specific nominative singular case endings -us (masculine) and -a (feminine).

Etymology from Wiktionary, CC BY-SA 3.0