al·​um | \ ˈa-ləm How to pronounce alum (audio) \

Definition of alum

 (Entry 1 of 3)

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
\ ə-ˈləm How to pronounce alum (audio) \

Definition of alum (Entry 2 of 3)

: alumnus, alumna a Yale alum

Definition of alum (Entry 3 of 3)

Is it acceptable to use alum for alumnus or alumna?

Noun (2)

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.

First Known Use of alum

Noun (1)

14th century, in the meaning defined at sense 1

Noun (2)

1877, in the meaning defined above

History and Etymology for alum

Noun (1)

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

Noun (2)

by shortening

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

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Cite this Entry

“Alum.” The Dictionary, Merriam-Webster Inc., Accessed 23 January 2020.

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More Definitions for alum


al·​um | \ ˈa-ləm How to pronounce alum (audio) \

Kids Definition of alum

: either of two aluminum compounds that are used especially in medicine (as to stop bleeding)


al·​um | \ ˈal-əm How to pronounce alum (audio) \

Medical Definition of alum

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

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More from Merriam-Webster on alum

Rhyming Dictionary: Words that rhyme with alum

Spanish Central: Translation of alum

Nglish: Translation of alum for Spanish Speakers Encyclopedia article about alum

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out of the ordinary or unreasonable

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