# unstable

> English word · Adjective · IPA /ʌnˈsteɪ.bəl/ · frequency rank #8,741

## Definitions
1. Not stable.
2. Having a strong tendency to change.
3. Fluctuating; not constant.
4. Fickle.
5. Unpredictable.
6. Readily decomposable.
7. Radioactive, especially with a short half-life.

## Etymology
From Middle English unstable; equivalent to un- (not) + stable.

## Easily confused with
- **usable** (https://plainspell.com/en/vs/unstable-vs-usable)
- **unusable** (https://plainspell.com/en/vs/unstable-vs-unusable)
- **unsuitable** (https://plainspell.com/en/vs/unstable-vs-unsuitable)
- **unable** (https://plainspell.com/en/vs/unable-vs-unstable)

## Common misspellings (13)
`nustable`, `unnstable`, `unsatble`, `unsstable`, `unstabble`, `unstabel`, `unstablle`, `unstalbe`, `unstbale`, `unstible`, `unsttable`, `untsable`, `usntable`

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