Etymology
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alum (n.)

"whitish mineral salt used as an astringent, dye, etc.," late 14c., from Old French alum, alun, from Latin alumen "alum," also "the alum plant," from Proto-Italic *alu- "bitter substance" literally "bitter salt," cognate with Greek aludoimos "bitter" and perhaps with English ale and some Balto-Slavic words for "beer" (such as Lithuanian alus). The plant's medicinal use on wounds was known to Pliny.

updated on September 18, 2022

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Definitions of alum from WordNet

alum (n.)
a white crystalline double sulfate of aluminum: the ammonium double sulfate of aluminum;
Synonyms: ammonia alum / ammonium alum
alum (n.)
a white crystalline double sulfate of aluminum: the potassium double sulfate of aluminum;
Synonyms: potassium alum / potash alum
alum (n.)
a person who has received a degree from a school (high school or college or university);
Synonyms: alumnus / alumna / graduate / grad
alum (n.)
a double sulphate of aluminum and potassium that is used as an astringent (among other things);
Etymologies are not definitions. From wordnet.princeton.edu, not affiliated with etymonline.