alum

1 of 3

noun (1)

al·​um ˈa-ləm 

1

: 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

2

: any of various double salts isomorphous with potassium aluminum sulfate

3

: aluminum sulfate

alum

2 of 3

noun (2)

ə-ˈləm 

: alumnus, alumna

a Yale alum

alum

3 of 3

abbreviation

aluminum

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

Noun

Under 30 alum Kimberley Ho walked away from her Wall Street career to launch Evereden for Generation Alpha. —Maggie McGrath, Forbes.com, 27 June 2025

Other voice actors in the new series include Veep star Tony Hale as Ultron, Saturday Night Live alum Vanessa Bayer as Swarm, and Talon Warburton (son of Seinfeld star Patrick Warburton) as Absorbing Man. —Katie Atkinson, Billboard, 26 June 2025

Bachelor Nation alum Rachel Recchia isn't giving up on love. —Allison Degrushe Published, EW.com, 26 June 2025

The event featured a wedding cake made by The Great American Baking Show alum Dana Commandatore, food from local vendors and a performance by DiscoFox, a band that Tombul met on a flight to visit Cooper in Budapest. —Emy Lacroix, People.com, 26 June 2025

Word History

Etymology

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

Rhymes for alum

• balam
• clallam
• kalam
• malum
• corallum
• paspalum

Kids Definition

alum

noun

al·​um

ˈal-əm

1

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

2

: aluminum sulfate

Medical Definition

alum

noun

al·​um ˈal-əm 

1

: either of two colorless or white crystalline double sulfates of aluminum used in medicine internally as emetics and locally as astringents and styptics:

a

: one KAl(SO₄)₂·12H₂O that is a sulfate of aluminum and potassium

called also potassium alum

b

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

called also ammonia alum, ammonium alum

2

: any of various double salts isomorphous with potassium aluminum sulfate