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



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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 Around the Mediterranean a line of unstable or failed states stretches from the Middle East to north Africa. The Economist, "Charlemagne Europe still lacks a foreign policy," 1 Aug. 2020 Why grumble about a 401(k) when so much is so unstable? Susan Tompor, Detroit Free Press, "Does a 401(k) plan still make sense for you? It might, or might not," 31 July 2020 While surprised by his arrival, Wendy was glad to see her little brother, but Ben's unstable nature would soon begin causing trouble for the family's money-laundering operation. Derek Lawrence, EW.com, "Ozark stars Laura Linney and Tom Pelphrey on Wendy and Ben's 'great tragedy': 'I was just crying'," 13 July 2020 Over the last few weeks two very different books have told the story of an unstable president unable to govern and unfit to lead. Molly Jong-fast, Vogue, "John Bolton and Mary Trump Seem to Agree On One Thing: Donald Trump Is a Truly Awful Person," 11 July 2020 There's an additional mention of using muons, heavier (if unstable) relatives of the electron and positron, for the collisions, something that's being actively pursued at the US' Fermilab. John Timmer, Ars Technica, "Europe officially sets its sights on a giant LHC successor," 25 June 2020 Somewhere in that gap, matter becomes unstable and collapses into a black hole—and neutron stars exist right on the threshold of that limit. Nadia Drake, National Geographic, "Mysterious cosmic object swallowed by black hole baffles astronomers," 24 June 2020 Still, the meal delivery business remains unstable. Michelle Cheng, Quartz, "Uber’s lost deal for Grubhub is still a huge step for the food delivery sector," 15 June 2020 Warmer water provides more fuel for storms & are also associated with more unstable atmosphere & lower pressure. Jeff Berardelli, CBS News, "Tropical Storm Fay makes landfall north of Atlantic City, lashing East Coast with heavy rain," 10 July 2020

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

3 Aug 2020

Cite this Entry

“Unstable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unstable. Accessed 12 Aug. 2020.

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More Definitions for unstable


How to pronounce unstable (audio)

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

Thesaurus: All synonyms and antonyms for unstable

Spanish Central: Translation of unstable

Nglish: Translation of unstable for Spanish Speakers

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