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adjective un·sta·ble \-ˈstā-bəl\

Simple Definition of unstable

  • : likely to change

  • : not emotionally or mentally healthy

  • : not held in a secure position : likely to move or fall

Full Definition of unstable

  1. :  not stable :  not firm or fixed :  not constant: 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

un·sta·ble·ness noun
un·sta·bly play \-b(ə-)lē\ adverb

Examples of unstable

  1. an unstable nuclear reactor core

  2. <the minute we put the books down on the unstable desk, the whole stack went crashing to the floor>

13th Century

First Known Use of unstable

13th century

Synonym Discussion of 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>.

Medical Dictionary


adjective un·sta·ble \-ˈstā-bəl\

Medical Definition of unstable

  1. :  not stable: asa:  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

Seen and Heard

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February 12, 2016

of, relating to, or suggestive of marble

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