un·sta·ble | \ ˌən-ˈstā-bəl \

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 \ adverb

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

Indeed no fish today, speaking generally of salmon, so fuses abundance and scarcity into an unstable and volatile paradox. Richard Adams Carey, WSJ, "‘Kings of the Yukon’ Review: A Song for the Salmon," 25 May 2018 Koniecza explained the quake left big gaps between the stones, causing the pyramid to be unstable. Katherine Lam, Fox News, "Mexico earthquake uncovers ancient temple hidden in damaged pyramid," 12 July 2018 Delimitros said the man seemed to be unstable and was taken into custody for evaluation. Karen Kucher, sandiegouniontribune.com, "Man wearing panda sweatshirt arrested after being found inside zoo gift store," 26 June 2018 There were no eruptions overnight, but the O'Neal said the situation is still unstable. CBS News, "Hawaii Kilauea volcano eruption: More Big Island residents told to be prepared to evacuate," 11 May 2018 And one of those priceless Tiffany windows was so unstable it’s currently being repaired by experts in Bryn Mawr, to the tune of $200,000. Anya Van Wagtendonk, Philly.com, "To save the world, first they must save a building in West Philly," 12 July 2018 In Venezuela itself, foreign regime change could easily result in the rise of a regime that's at least as unstable as the Maduro government. Rick Noack, Washington Post, "The many problems with Trump’s reported idea of invading Venezuela," 5 July 2018 It’s been reported that Tunisia, a country that has been relatively unstable since the Arab Spring began in 2011, is also a hotspot for exporting hair. refinery29.com, "Death Threats & $3 Ponytails: What The Fake Hair Trade Is Hiding," 9 June 2018 The office could, for instance, require schools that appear to be financially unstable or on the brink of closing to create contingency plans for how students would finish their degrees elsewhere. Laura Krantz, BostonGlobe.com, "After Mount Ida, AG seeks tougher college oversight," 25 May 2018

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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Statistics for unstable

Last Updated

17 Sep 2018

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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 \

Kids Definition of unstable

: not stable an unstable boat


un·sta·ble | \ -ˈstā-bəl \

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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Comments on unstable

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