unstable
- 01 B2 Upper Intermediate
adj.likely to fall, move, or collapse because it is not firm.
adj.lacking physical stability or equilibrium; precarious in position or structure.
Simple“Don't climb that ladder; it looks very unstable on this uneven ground.”
In context“The engineers warned that the bridge's foundations were becoming unstable due to the constant erosion of the riverbed.”
- 02 B2 Upper Intermediate
adj.changing often and without warning, like the weather or a country's politics.
adj.prone to sudden or unpredictable change; lacking a constant or reliable state.
Simple“The political situation in the region remains unstable after the recent elections.”
In context“Economists are concerned that the unstable market conditions will discourage long-term investment in the manufacturing sector.”
SynonymsAntonyms - 03 B2 Upper Intermediate
adj.having moods or feelings that change very quickly or in a worrying way.
adj.characterised by emotional or mental volatility; prone to sudden shifts in temperament.
Simple“He has been emotionally unstable since he lost his job last month.”
In context“The witness was deemed unreliable due to her unstable mental state at the time of the incident.”
Synonyms - 04 C1 Advanced
adj.likely to change its form or explode easily.
adj.readily undergoing chemical decomposition or change; highly reactive.
Simple“The scientist handled the unstable liquid with great care in the lab.”
In context“Certain chemical compounds become highly unstable when exposed to direct sunlight or sudden changes in temperature.”
- 05 C1 Advanced
adj.having a nucleus that changes and releases energy.
adj.relating to an atomic nucleus that is prone to spontaneous radioactive decay.
Simple“Unstable isotopes break down over time and release radiation.”
In context“The laboratory specialises in measuring the decay rates of unstable atomic nuclei produced during fission.”
SynonymsAntonyms - 06 C2 Proficiency
v.to let an animal, like a horse, out of its building.
v.to release an animal from a stable. Transitive use.
Simple“The groom went to unstable the horses for the morning ride.”
In context“At the first sign of fire, the stable hands rushed to unstable the panicked stallions and lead them to the safety of the paddock.”
Usage concurrent unstable · highly unstable · unstable condition
“Importantly, never exercise on unstable surfaces when you’re tired.”
“Type Ia supernovae are extremely bright explosions that are generally believed to occur when a white dwarf becomes unstable and undergoes a runaway thermonuclear reaction.”
From Middle English unstable; equivalent to un- (not) + stable.
From un- (reversive prefix) + stable.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.