# alum

> English word · Noun · IPA /ˈæl.əm/ · frequency rank #20,832

## Definitions
1. An astringent salt, usually occurring in the form of pale crystals, much used in the dyeing and tanning trade and in certain medicines, and now understood to be a double sulphate of potassium and aluminium (K₂SO₄·Al₂(SO₄)₃·24H₂O).
2. Any similar double sulphate in which either or both of the potassium and aluminium is wholly or partly replaced by other univalent or tervalent cations.

## Etymology
From Middle English alum, alum, alym, alyme, from Anglo-Norman alum, alun, from Latin alūmen.

## Easily confused with
- **AM** (https://plainspell.com/en/vs/alum-vs-am)
- **AU** (https://plainspell.com/en/vs/alum-vs-au)
- **arm** (https://plainspell.com/en/vs/alum-vs-arm)
- **ATM** (https://plainspell.com/en/vs/alum-vs-atm)
- **aux** (https://plainspell.com/en/vs/alum-vs-aux)
- **aud** (https://plainspell.com/en/vs/alum-vs-aud)
- **ASU** (https://plainspell.com/en/vs/alum-vs-asu)
- **asm** (https://plainspell.com/en/vs/alum-vs-asm)
- **APM** (https://plainspell.com/en/vs/alum-vs-apm)
- **AUC** (https://plainspell.com/en/vs/alum-vs-auc)
- **atom** (https://plainspell.com/en/vs/alum-vs-atom)
- **aqua** (https://plainspell.com/en/vs/alum-vs-aqua)
- **anus** (https://plainspell.com/en/vs/alum-vs-anus)
- **Arun** (https://plainspell.com/en/vs/alum-vs-arun)
- **ASTM** (https://plainspell.com/en/vs/alum-vs-astm)
- **Aram** (https://plainspell.com/en/vs/alum-vs-aram)
- **Alva** (https://plainspell.com/en/vs/alum-vs-alva)
- **Alun** (https://plainspell.com/en/vs/alum-vs-alun)
- **annum** (https://plainspell.com/en/vs/alum-vs-annum)
- **asylum** (https://plainspell.com/en/vs/alum-vs-asylum)

## Common misspellings (5)
`allum`, `almu`, `alumm`, `aulm`, `laum`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/alum