alum

¹ American  

[al-uhm] / ˈæl əm /

noun

Chemistry.

1. Also called potassium alum.  Also called potash alum.  a crystalline solid, aluminum potassium sulfate, K 2 SO 4 ⋅Al 2 (SO4 ) 3 ⋅24H 2 O, used in medicine as an astringent and styptic, in dyeing and tanning, and in many technical processes.

2. one of a class of double sulfates analogous to aluminum potassium sulfate, as aluminum ammonium sulfate, having the general formula R 2 SO 4 ⋅X 2 (SO4 ) 3 ⋅24H 2 O, where R is a univalent alkali metal or ammonium, and X one of a number of trivalent metals.

3. (not in technical use) aluminum sulfate.

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alum ² American  

[uh-luhm] / əˈlʌm /

noun

Informal.

1. an alumna or alumnus.

   Nearly 45 of us alums went on a day trip on the river to celebrate graduation.

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alum. ³ American  

abbreviation

Chemistry.

1. aluminum.

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alum British  

/ ˈæləm /

noun

1. Also called: potash alum.  a colourless soluble hydrated double sulphate of aluminium and potassium used in the manufacture of mordants and pigments, in dressing leather and sizing paper, and in medicine as a styptic and astringent. Formula: K 2 SO 4 .Al 2 (SO 4 ) 3 .24H 2 O

2. any of a group of isomorphic double sulphates of a monovalent metal or group and a trivalent metal. Formula: X 2 SO 4 .Y 2 (SO 4 ) 3 .24H 2 O, where X is monovalent and Y is trivalent

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alum Scientific  

/ ăl′əm /

1. Any of various crystalline double salts of a trivalent metal (such as aluminum, chromium, or iron) and a monovalent metal (such as potassium or sodium), especially aluminum potassium sulfate. Alum is widely used in industry as a hardener and purifier, and in medicine as an emetic and to stop bleeding.

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Usage

What’s the difference between alum, alumnus, and alumni? The informal word alum refers to a graduate of a school, such as a high school or university. It’s a shortening of alumnus or alumna.In Latin, alumnus specifically refers to a male graduate, and sometimes this distinction is carried into English, with alumna being used to refer to a female graduate. The plural of alumna is alumnae.The plural of alumnus is alumni (which follows the plural ending construction used in other Latin-derived words, like stimulus and stimuli). Still, alumnus and alumni are both commonly used in a gender-neutral way.Alum is also used regardless of gender. It’s sometimes pluralized as alums.Here’s an example of alum and alumni used correctly in the same sentence.Example: As an alum, you share something with all of the alumni, regardless of when each of you graduated. Want to learn more? Read the breakdown of the difference between alumnus and alumni.

Gender

What's the difference between alum, alumnus, and alumna? See alumnus.

Etymology

Origin of alum¹

First recorded in 1275–1325; Middle English < Anglo-French, from Latin alūmen; replacing Old English alefne, ælifnæ, from Old Welsh (compare Medieval Welsh elyf ) < Latin alūmini- (stem of alūmen )

Origin of alum²

First recorded in 1875–80; by shortening

Example Sentences

A pole vaulter and cheerleader at the University of North Texas, Delka was introduced to skeleton by Johnny Quinn, a fellow North Texas alum who competed in the bobsled.

From Los Angeles Times

Musk’s ties to Morgan Stanley run deep—both his money manager, Jared Birchall, and the chief financial officer of xAI, Anthony Armstrong, are bank alums.

From The Wall Street Journal

An alum now at Long Beach City College led the march, joined by adults from Safe Passage and other community groups.

From Los Angeles Times

The “Scandal” alum in a Monday Instagram post encouraged viewers to call their senators as she modeled the behavior on camera.

From Los Angeles Times

They knew they wanted to cast an American and the idea of hiring a “Mad Men” alum was incredibly appealing, considering they are huge fans.

From Los Angeles Times

Related Words

• alumna
• alumnus
• doctor
• grad
• recipient