alum

¹

[al-uhm]

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.

alum

²

[uh-luhm]

noun

Informal.

1. an alumna or alumnus.

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

alum.

³

abbreviation

Chemistry.

1. aluminum.

alum

/ 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

alum

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.

Gender Note

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

Word History and Origins

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

Word History and Origins

Origin of alum¹

C14: from Old French, from Latin alūmen

Example Sentences

The “Saturday Night Live” alum recounted the incident from his hospital bed during Tuesday’s episode of the “Lonely Island & Seth Meyers” podcast.

From Los Angeles Times

Former Villanova coach Jay Wright wrote on social media that Raveling was “the finest human being, inspiring mentor, most loyal alum and a thoughtful loving friend.”

From Los Angeles Times

But I also hear your own family was involved, as well as some “Rez Dogs” alums.

From Los Angeles Times

He’s like, ‘I didn’t even recognize you. I thought you were an alum.’

From Los Angeles Times

An experiment intended to rid “The Real Housewives of Beverly Hills” alum Brandi Glanville of a facial parasite left the former reality TV star with chemical burns.

From Los Angeles Times

Related Words

• alumna 
• alumnus 
• doctor 
• grad 
• recipient 

When To Use

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.