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

Both ice giants’ magnetic fields are suspected of being unstable. National Geographic, "Bizarre form of hot ice seen on Earth," 8 May 2019 Journaling also helps me reduce any stress and or anxiety that may come with a life that is often seen from the outside as being unstable. Annie Daly, SELF, "16 Ways to Stay Mentally Healthy When You Travel A LOT, From People Who Do It," 6 Dec. 2018 The atmosphere turned extremely unstable because of the colliding air masses. Jason Samenow, Washington Post, "The weather in the Middle East has gone haywire because of a freak storm," 27 Apr. 2018 The Vermont Department of Public Safety said the recent storms have created ‘‘extremely unstable conditions in steep terrain.’’ The US Army’s Mountain Warfare school is run by the Vermont National Guard. Globe Staff, BostonGlobe.com, "New England news in brief," 15 Mar. 2018 Boston’s situation going into the draft appears unstable, with reports indicating that Kyrie Irving and now Al Horford will be on the way out. Jeremy Woo, SI.com, "2019 NBA Mock Draft 12.0: Trade Rumors and Final Projections," 20 June 2019 But because some parts of these superconductors are unstable, like their Cooper pairs of electrons, these super strong magnets have their limits. David Grossman, Popular Mechanics, "This Is the Strongest Superconducting Magnet Ever," 19 June 2019 Brown coal is dirty and unstable, and the lives of those associated with it are liable to be equally volatile. The Economist, "What caused Australia’s devastating bushfires?," 15 June 2019 Their relationship was fiery and unstable, in the way that intensely passionate but ultimately destructive relationships can be. Kayla Webley Adler, Marie Claire, "I Was One Of The Top Doctors In My Field. I Was Also An Opioid Addict.," 25 Feb. 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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Statistics for unstable

Last Updated

9 Jul 2019

Look-up Popularity

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

Comments on unstable

What made you want to look up unstable? Please tell us where you read or heard it (including the quote, if possible).


an act or instance of editing or removing

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