Alum

How to spell alum

4 letters · 2 syllables

How to pronounce alum

Say the part in capitals loudest.

What does alum mean?

1. nounA crystalline mineral salt, typically potassium aluminium sulfate, used in water purification, dyeing, and as a styptic to stop bleeding.
2. nounAn informal term for a graduate or former student of a school, college, or programme, used for either sex.

Alum in a sentence

• The barber kept a block of alum to seal shaving nicks.

• As a proud alum of the university, she donates to the scholarship fund each year.

• Adding a little alum helps clarify cloudy water before filtering.

• The company hired a recent alum of the coding bootcamp.

Where does alum come from?

Language of origin: Latin

In its older and primary sense, alum comes from the Latin alumen, the name for a bitter, astringent mineral salt that the Romans valued for fixing dyes and for staunching small cuts. English took the word in the 1300s through Old French alum, keeping both the spelling and the chemical meaning largely intact. The same Latin root is thought to connect with words for bitterness and may be distantly related to the element name aluminium, which the chemist Humphry Davy coined in the early 1800s from the very same alumen. A quite separate modern sense arose in American English in the late 1800s, where alum is simply a casual clipping of the Latin alumnus (a male graduate) or alumna (a female graduate); that informal use spread because it neatly sidesteps having to choose a gendered Latin ending. The shared four letters are a coincidence of clipping rather than meaning, which is why one alum can purify water while another attends a college reunion.

How the word is built

• alum (from Latin alumen, a bitter mineral salt); the graduate sense is a clipped form of alumnus / alumna