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

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>

First Known Use of UNSTABLE

13th century


adjective un·sta·ble \-ˈstā-bəl\   (Medical Dictionary)

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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