# unstable

/ənˈsteɪbəɫ/ (US) · /ʌnstˈeɪbəl/ (UK)

Source: https://englishreference.com/word/unstable
Updated: 2026-06-20

## Senses

### 1. physically shaky

adjective · CEFR B2

likely to fall, move, or collapse because it is not firm.

For teachers: lacking physical stability or equilibrium; precarious in position or structure.

- Don't climb that ladder; it looks very unstable on this uneven ground.
- The engineers warned that the bridge's foundations were becoming unstable due to the constant erosion of the riverbed.

### 2. likely to change suddenly

adjective · CEFR B2

changing often and without warning, like the weather or a country's politics.

For teachers: prone to sudden or unpredictable change; lacking a constant or reliable state.

- The political situation in the region remains unstable after the recent elections.
- Economists are concerned that the unstable market conditions will discourage long-term investment in the manufacturing sector.

### 3. emotionally volatile

adjective · CEFR B2

having moods or feelings that change very quickly or in a worrying way.

For teachers: characterised by emotional or mental volatility; prone to sudden shifts in temperament.

- He has been emotionally unstable since he lost his job last month.
- The witness was deemed unreliable due to her unstable mental state at the time of the incident.

### 4. chemically reactive

adjective · CEFR C1 · Technical

likely to change its form or explode easily.

For teachers: readily undergoing chemical decomposition or change; highly reactive.

- The scientist handled the unstable liquid with great care in the lab.
- Certain chemical compounds become highly unstable when exposed to direct sunlight or sudden changes in temperature.

### 5. radioactive

adjective · CEFR C1 · Technical

having a nucleus that changes and releases energy.

For teachers: relating to an atomic nucleus that is prone to spontaneous radioactive decay.

- Unstable isotopes break down over time and release radiation.
- The laboratory specialises in measuring the decay rates of unstable atomic nuclei produced during fission.

### 6. to release from a stable

verb · CEFR C2 · Archaic

to let an animal, like a horse, out of its building.

For teachers: to release an animal from a stable. Transitive use.

- The groom went to unstable the horses for the morning ride.
- At the first sign of fire, the stable hands rushed to unstable the panicked stallions and lead them to the safety of the paddock.

## Examples

- The old wooden ladder feels very unstable.
- The country's economy remained unstable for years following the sudden collapse of its largest bank.
- Chemical compounds that are highly unstable must be stored at extremely low temperatures to prevent them from reacting or decomposing unexpectedly.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.