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

For tweeting the wrong thing, for not making enough cars, for appearing unstable. Popular Mechanics Editors, Popular Mechanics, "In Defense of Elon Musk," 16 Oct. 2018 The city also has notoriously bad subsoil conditions, and developers often build on unstable land. Frank Miles, Fox News, "Controversial Mexico City shopping mall partially collapses," 12 July 2018 That suggests that regardless of whether a deal is struck on the UK’s terms or the EU’s, it is bound to prove highly unstable. Simon Nixon, WSJ, "Britain’s Brexit Dilemma: Should It Compromise, or Confront the EU?," 4 July 2018 Yet the grandeur of Germania is capsizing under unstable soil, foundations slowly buckling, cracks appearing in walls; just as the sinking prototype Schwerbelastungskörper suggested. Darran Anderson, The Atlantic, "The Cities That Never Existed," 17 June 2018 Disney Channel star Ross Lynch is subversively cast against type as Dahmer, while Anne Heche unravels as his unstable mother. Chris Ball, cleveland.com, "'My Friend Dahmer,' now on DVD and Blu-ray (review)," 15 Apr. 2018 Rescuers then dug 30 feet under unstable debris to save the 32-year-old woman, who was the last survivor recovered from the World Trade Center site. Alexandra Gekas, Woman's Day, "10 Amazing Animal Rescue Stories," 10 Jan. 2011 The unstable ground makes earthquakes more dangerous; during the destructive temblor on 19 September 2017, an elementary school collapsed in Tlalpan. Lizzie Wade, Science | AAAS, "Can this environmental engineer—now elected mayor—fix Mexico City?," 2 July 2018 And kids whose lives are unstable, who are bounced around, who lack supportive adults in their lives are kids who, far too often, are on paths to difficulties. Milwaukee Journal Sentinel, "Borsuk: What would Mister Rogers say about the images of kids at the southern border?," 22 June 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

12 Nov 2018

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 \

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

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


an inexhaustible supply or amount

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