Alum or alumnus?
alum is a noun meaning “Any similar double sulphate in which either or both of the potassium and…”; alumnus is a noun meaning “A male pupil or student”. In written English (wordfreq, 2021 data) alum is about 2.2 times as common as alumnus.
What is the difference between alum and alumnus?
| alum | alumnus | |
|---|---|---|
| Part of speech | noun, verb | noun |
| Meaning | An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to… Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations To steep in, or otherwise impregnate with, a solution of alum; to treat with alum | A male pupil or student A male graduate |
| Example | none recorded | none recorded |
| Forms | alums alums, alumni | alumni, alumnuses |
| Pronunciation | /ˈæl.əm/ /əˈlʌm/ | /əˈlʌmnəs/ |
| In writing | 1.8 times per million words | about once in every 1 million words |
Sources: alum and alumnus in the English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0); written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
Every current meaning of alum and alumnus
alum
- 1
An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and…
- 2
To steep in, or otherwise impregnate with, a solution of alum; to treat with alum
- 3
CanadaUSA past attendee or graduate (of any gender) of a college, university or other educational institution
- 4
Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations
alumnus
- 1
A male pupil or student
- 2
A male graduate
- 3
A student of any gender
- 4
A graduate of any gender
Source: the English Wiktionary, dump of September 2, 2026 (CC BY-SA 4.0); obsolete, archaic, dialect and rare senses left out.
Which is more common, alum or alumnus?
alum appears 1.8 times per million words; alumnus about once in every 1 million words.
alum 1.8 times per million wordsalumnus about once in every 1 million words
Source: written frequency: wordfreq 3.1 (a 2021 snapshot of Wikipedia, subtitles, news, books, web text and social media).
How many people search alum vs alumnus?
“alum vs alumnus” is searched about 30 times a month on Bing (Google reports it together with close variants, so it has no figure of its own) in the United States.
Sources: Google Ads keyword data through DataForSEO and Microsoft Advertising keyword data through DataForSEO, the average month from September 2025 to August 2026.