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 unstable (audio) \ adverb

Synonyms & Antonyms for unstable



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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 political situation in the West is, at best, unstable. Ew Staff, EW.com, "Read the first three chapters of Kathy Wang's new spy thriller Impostor Syndrome," 27 Apr. 2021 Dexter's fur was dry and clumped together, and Goliath's eyes were cloudy and his rear legs were unstable. Taylor Pettaway, San Antonio Express-News, "Tiger, bobcat found inside South Side home; 2 arrested for animal cruelty," 26 Apr. 2021 Under Indiana’s red flag law, the authorities have two weeks after taking someone’s weapon to argue before a judge that the person is unstable and should be barred from possessing a gun for a period of time. BostonGlobe.com, "FedEx gunman bought two rifles after police seized his shotgun, chief says," 18 Apr. 2021 This model presently contains a couple dozen particles, but most of them are unstable and therefore can’t be found just by looking at the matter that normally surrounds us. Sabine Hossenfelder, Scientific American, "Is the Standard Model of Physics Now Broken?," 7 Apr. 2021 That may not sound like a very heavy kettlebell, but again, sand is unstable, which contributes to the challenge, and its straps are less stable than a rigid handle. Wes Siler, Outside Online, "How to Build a Home Gym for Less than a Membership," 29 Mar. 2021 Germany is less unstable, but calls for reform still ring true with roughly four in 10. Philip Elliott, Time, "Think the System Is Broken? You’re Not Alone," 31 Mar. 2021 The Zumwalt's unique bow—which angles downward instead of upward—has led to allegations the ship could be unstable in rough seas. Kyle Mizokami, Popular Mechanics, "Good News: The USS Zumwalt Can Stay Afloat in Rough Seas," 17 Mar. 2021 Scally decided that Hingst was mentally unstable, rather than a scam artist. Helen Lewis, The Atlantic, "The Identity Hoaxers," 16 Mar. 2021

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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Time Traveler for unstable

Time Traveler

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

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Statistics for unstable

Last Updated

30 Apr 2021

Cite this Entry

“Unstable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unstable. Accessed 9 May. 2021.

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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

More from Merriam-Webster on unstable

Thesaurus: All synonyms and antonyms for unstable

Nglish: Translation of unstable for Spanish Speakers

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