Word
unstable
Phoneticsun·sta·ble, stress on the second syllable
US/ənˈsteɪbəɫ/
UK/ʌnstˈeɪbəl/
Definitions
01physically shaky
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.
“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.”
Synonyms
02likely to change suddenly
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.
“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.”
Synonyms
Antonyms
03emotionally volatile
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.
“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.”
Synonyms
04chemically reactive
C1 · Advanced Science Technical
adj. likely to change its form or explode easily.
adj. 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.”
05radioactive
C1 · Advanced Science Technical
adj. having a nucleus that changes and releases energy.
adj. 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.”
Synonyms
Antonyms
06to release from a stable
C2 · Proficiency Archaic
v. to let an animal, like a horse, out of its building.
v. 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.”
Antonyms
Collocations
Common phrases and expressions where native English speakers use the word “unstable” in context.
Adjective
01. highly unstable
“The chemical compound is highly unstable and must be handled with extreme care.”
adv + adj
02. unstable condition
“The patient remains in an unstable condition following the emergency surgery.”
adj + noun
03. concurrent unstable
Real-World Examples
“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.” “If the fire is intense enough and the atmosphere is unstable, the cloud can continue expanding upward into the upper troposphere.” “The researchers believe the shipment sank during a particularly unstable period in Mediterranean history.” Etymology
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.
Domains
- Exam level
- CambridgeCambridgeCambridge English QualificationsThe exam suite from Cambridge University Press & Assessment, from A1 Movers up to C2 Proficiency. The benchmark names double as CEFR labels.B2 FirstIELTSIELTSInternational English Language Testing SystemThe 0–9 band test co-owned by the British Council, IDP, and Cambridge. Used for university entry, work, and migration.5.5–6.5TOEFL iBTTOEFL iBTTest of English as a Foreign Language, Internet-Based TestETS's academic English test, the standard route for US university admissions. Scored 0–120, with a 1–6 scale since 2026.1–6 scale: 4.0–4.572–94TOEICTOEICTest of English for International CommunicationETS's workplace English test, big in Japan and Korea. Listening & Reading scores 10–990 and tops out at C1.785–944
- Frequency
- Frequent
- Level
- B2 · Upper Intermediate
- Updated
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