alum

¹

[ al-uhm ]

noun

, Chemistry.

1. Also called potash alum, a crystalline solid, aluminum potassium sulfate, K 2 SO 4 ⋅Al 2 (SO 4 ) 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 (SO 4 ) 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 ( def ).

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 for

, Chemistry.

1. aluminum.

alum

/ ˈæləm /

noun

1. Also calledpotash 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

/ 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.

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

Natasha Strain, an alum of the campus who works as a childcare worker and supervisor at the facility, is one of the plaintiffs listed in the suit.

From Voice of San Diego

For Top Chef, that meant many challenges that took advantage of outdoor kitchens, a bubble of all-star alums replacing the usual rotating cast of guest judges and a brand-new approach to viewers’ beloved Restaurant Wars.

From Time

She is currently a senior director at Fairmont Consulting Group, a boutique management consulting firm in the aerospace and defense sector founded by fellow alums Jay Wynn, MBA ’04, and Ben Harper, MBA ’08, SM ’08.

From MIT Technology Review

In their MHS homes, alums said they were ranked by how well they did their chores and followed rules.

From ProPublica

Natasha Strain, an alum of the campus, works as a childcare worker and supervisor at the facility.

From Voice of San Diego

A TNR alum dives deep in what happened with the 100-year-old institution.

From The Daily Beast

And those who take issue with the ice bucket challenge have found an unexpected spokesperson in Jackass alum Steve-O.

From The Daily Beast

Marine friends, all ranks and all mostly Anbar fighting alum, have been sending me emails as well.

From The Daily Beast

Apple alum Tony Fadell reinvented the boring market for home thermostats with his sleek and eco-savvy digital Nest.

From The Daily Beast

Petraeus, himself a Sosh alum, became the central figure for a mix of reasons.

From The Daily Beast

If they require a second water put alum to that also as well as to the rinsing and blue water.

From Project Gutenberg

Thus the proportions are omitted, and alum becomes alum compound, whatever that may mean.

From Project Gutenberg

On examination it was found that the enclosure of the Atarrea was broken down, and the source saturated with alum.

From Project Gutenberg

The principal impurity, and one which renders alum unfit for the use of the dyer, is iron.

From Project Gutenberg

The applications of alum in the arts and manufactures are numerous and important.

From Project Gutenberg

Related Words

• alumna
• alumnus
• doctor
• grad
• recipient

Alum Vs. Alumnus Vs. Alumni Vs. Alumna Vs. Alumnae

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.

Quiz yourself on alum vs. alumnus!

True or False? 

Alum and alumnus are both always used in a gender-neutral way.