adjective un·sta·ble \-ˈstā-bəl\

: likely to change

: not emotionally or mentally healthy

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

Full Definition of UNSTABLE

:  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 \-b(ə-)lē\ adverb

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>.
UNSTABLE Defined for Kids


adjective un·sta·ble \ˌən-ˈstā-bəl\

Definition of UNSTABLE for Kids

:  not stable <an unstable boat>
Medical Dictionary


adjective 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


Next Word in the Dictionary: unstable anginaPrevious Word in the Dictionary: unstabilityAll Words Near: unstable
How to use a word that (literally) drives some people nuts.
Test your vocab with our fun, fast game
Ailurophobia, and 9 other unusual fears