un·​sta·​ble | \ ˌən-ˈstā-bəl How to pronounce unstable (audio) \

Definition of unstable

: not stable : not firm or fixed : not constant: such as
a : not steady in action or movement : irregular an unstable pulse
b : wavering in purpose or intent : vacillating
c : lacking steadiness : apt to move, sway, or fall an unstable tower
d(1) : liable to change or alteration an unstable economy unstable weather
(2) : readily changing (as by decomposing) in chemical or physical composition or in biological activity
e : characterized by lack of emotional control

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Other Words from unstable

unstableness noun
unstably \ ˌən-​ˈstā-​b(ə-​)lē How to pronounce unstably (audio) \ adverb

Synonyms & Antonyms for unstable


unbalanced, unsteady


balanced, equilibrated, stabilized, stable, steady

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Choose the Right Synonym for unstable

inconstant, fickle, capricious, mercurial, unstable mean lacking firmness or steadiness (as in purpose or devotion). inconstant implies an incapacity for steadiness and an inherent tendency to change. an inconstant friend fickle suggests unreliability because of perverse changeability and incapacity for steadfastness. performers discover how fickle fans can be capricious suggests motivation by sudden whim or fancy and stresses unpredictability. an utterly capricious critic mercurial implies a rapid changeability in mood. made anxious by her boss's mercurial temperament unstable implies an incapacity for remaining in a fixed position or steady course and applies especially to a lack of emotional balance. too unstable to hold a job

Examples of unstable in a Sentence

an unstable nuclear reactor core the minute we put the books down on the unstable desk, the whole stack went crashing to the floor

Recent Examples on the Web

The pond took 10 months to dry out and was so unstable afterward that three feet of clay had to be hauled out and replaced with new soil, slowing progress again. Emily Young, Los Angeles Times, "Beloved Japanese garden reopens at Lotusland in Montecito — but good luck getting in," 26 July 2019 One warning about the unstable young man who’d been stockpiling guns and threatening to shoot up a school came on Jan 5, 2018. Susannah Bryan, sun-sentinel.com, "Parents of Parkland shooting victim sue FBI over bungled tips," 30 June 2019 Earlier in May, park officials warned visitors that rocks and snow near the edge of the caldera were unstable and could give way without warning. CNN, "Man rescued after falling 800 feet into Crater Lake in Oregon," 11 June 2019 In recent years, Joseph has taken his talents into some of the most unstable regions of the world, bringing gear and musical know-how to refugees and oppressed groups. Chris Bieri, Anchorage Daily News, "After teaching rock music in Kabul, songwriter Jerry Joseph turns toward optimism," 12 Apr. 2018 Nominally, his party, the right-wing Northern League, is the junior partner in an unlikely and unstable coalition government with the anti-establishment Five Star Movement (M5S). The Economist, "Will Matteo Salvini wreck the euro?," 11 July 2019 And even when some of people do have access the electricity supply is unreliable and unstable. Yinka Adegoke, Quartz Africa, "Solar’s big promise for lighting Africa is tied to the continent’s mobile money advantage," 30 June 2019 That could pinch Tucson, which currently gets its water from the Colorado River, though that resource is politically fraught and unstable. Douglas Main, National Geographic, "In a land of wild cats and scarce water, a battle over mining heats up," 25 Apr. 2019 Karadžic, who would go on to order the massacre of eight thousand Muslim Bosniaks at Srebrenica, emerges as an unstable yet intransigent demagogue caught in the grip of an ethnonationalist fever dream. Giles Harvey, Harper's magazine, "Home Truths," 10 Jan. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'unstable.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of unstable

13th century, in the meaning defined above

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Last Updated

6 Aug 2019

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Time Traveler for unstable

The first known use of unstable was in the 13th century

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More Definitions for unstable



English Language Learners Definition of unstable

: likely to change
: not emotionally or mentally healthy
: not held in a secure position : likely to move or fall


un·​sta·​ble | \ ˌən-ˈstā-bəl How to pronounce unstable (audio) \

Kids Definition of unstable

: not stable an unstable boat


un·​sta·​ble | \ -ˈstā-bəl How to pronounce unstable (audio) \

Medical Definition of unstable

: not stable: as
a : characterized by frequent or unpredictable changes a patient in unstable condition
b : readily changing (as by decomposing) in chemical composition or biological activity unstable compounds
c : characterized by lack of emotional control or stability

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More from Merriam-Webster on unstable

Rhyming Dictionary: Words that rhyme with unstable

Thesaurus: All synonyms and antonyms for unstable

Spanish Central: Translation of unstable

Nglish: Translation of unstable for Spanish Speakers

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