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noun (1)

al·​um ˈa-ləm How to pronounce alum (audio)
: a potassium aluminum sulfate KAl(SO4)2·12H2O or an ammonium aluminum sulfate NH4Al(SO4)2·12H2O used especially for its astringent and styptic properties
: any of various double salts isomorphous with potassium aluminum sulfate


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noun (2)

: alumnus, alumna
a Yale alum


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Did you know?

Is it acceptable to use alum for alumnus or alumna?

The words that we have used to refer to people who have attended or graduated from a school, college, or university have changed a bit over the past several centuries. Traditionally, the word alumnus has been used to refer to a single male, whereas alumna has been used for a single woman. Initially the plural forms were alumni to refer to multiple men (or multiple men and women) and alumnae for multiple women. A little over a hundred years ago the shortened form of alum began to be used to describe a graduate or past attendee of either gender. Although many people feel that alum is informal, it is in increasing use, and we appear to be moving toward a greater acceptance of the word. The plural of alum is alums.

Examples of alum in a Sentence

Recent Examples on the Web
The Total Bellas alum finished off the carousel with a photo of Matteo clad in a seasonal outfit — an orange Henley, a flannel and a pumpkin sticker — and concentrating on a waffle in front of him. Hannah Sacks, Peoplemag, 25 Nov. 2023 This Allure Best of Beauty alum is one of the most popular hair tools on the internet for its ability to curl, smooth, blowout, and polish hair effortlessly. Angela Trakoshis, Allure, 24 Nov. 2023 The spring event, still some three months away, is an opportunity for the Aztecs’ newest alums to turn the heads of NFL scouts. Kirk Kenney, San Diego Union-Tribune, 22 Nov. 2023 Leigh is the latest Coen movie alum to appear on the show, joining the likes of Billy Bob Thornton and Michael Stuhlbarg. Alan Sepinwall, Rolling Stone, 21 Nov. 2023 Opening with the playing of The Impossible Dream written by a Yale alum, last week, Yale hosted an Arab-Israeli diplomatic dialogue on campus that harkens to the first Thanksgiving, a dialogue that promoted harmony across cultural divides. Jeffrey Sonnenfeld, Fortune, 20 Nov. 2023 Dudamel is the program’s most accomplished alum and proselytizer — the Youth Orchestra Los Angeles, which was launched by the L.A. Phil in 2007, is modeled after El Sistema and has given free instruments and music education to the city’s underprivileged children, many of whom are Black or Latino. Fidel Martinez, Los Angeles Times, 16 Nov. 2023 The American Idol alum showcased her new hairstyle on The Kelly Clarkson Show Monday, where she was seen rocking her new wispy face-framing bangs. Charna Flam, Peoplemag, 14 Nov. 2023 On his recruiting trip to USC, Mirisch met with Cathedral Catholic alum Chris Sturtevant, who played on the Dons’ 2018 Open Division title team. Glae Thien, San Diego Union-Tribune, 13 Nov. 2023 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'alum.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Noun (1)

Middle English, from Anglo-French alum, alun, from Latin alumen

Noun (2)

by shortening

First Known Use

Noun (1)

14th century, in the meaning defined at sense 1

Noun (2)

1877, in the meaning defined above

Time Traveler
The first known use of alum was in the 14th century

Dictionary Entries Near alum

Cite this Entry

“Alum.” Dictionary, Merriam-Webster, Accessed 7 Dec. 2023.

Kids Definition


: either of two colorless crystalline compounds containing aluminum that are used in medicine (as to check local sweating or to stop bleeding)

Medical Definition


al·​um ˈal-əm How to pronounce alum (audio)
: either of two colorless or white crystalline double sulfates of aluminum used in medicine internally as emetics and locally as astringents and styptics:
: one KAl(SO4)2·12H2O that is a sulfate of aluminum and potassium

called also potassium alum

: one consisting of an ammonium aluminum sulfate NH4Al(SO4)2·12H2O

called also ammonia alum, ammonium alum

: any of various double salts isomorphous with potassium aluminum sulfate

More from Merriam-Webster on alum

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