unstable

[uhn-stey-buhl]
adjective
1.
not stable; not firm or firmly fixed; unsteady.
2.
liable to fall or sway.
3.
unsteadfast; inconstant; wavering: unstable convictions.
4.
marked by emotional instability: an unstable person.
5.
irregular in movement: an unstable heartbeat.
6.
Chemistry. noting compounds that readily decompose or change into other compounds.

Origin:
1175–1225; Middle English; see un-1, stable2

unstableness, noun
unstably, adverb


2. precarious. 2, 3. See unsettled. 3. vacillating.
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Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
unstable (ʌnˈsteɪbəl)
 
adj
1.  lacking stability, fixity, or firmness
2.  disposed to temperamental, emotional, or psychological variability
3.  (of a chemical compound) readily decomposing
4.  physics
 a.  (of an elementary particle) having a very short lifetime
 b.  spontaneously decomposing by nuclear decay; radioactive: an unstable nuclide
5.  electronics (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation
 
un'stableness
 
n
 
un'stably
 
adv

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Etymonline
Word Origin & History

unstable
early 13c., "apt to move," from un- (1) "not" + stable (adj.). Cf. M.H.G. unstabel. Meaning "liable to fall" is recorded from c.1300; sense of "fickle" is attested from late 13c.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
unstable   (ŭn-stā'bəl)  Pronunciation Key 
  1. Liable to undergo spontaneous decay into some other form. For example, the nucleus of uranium 238 atom is unstable and changes by radioactive decay into the nucleus of thorium 234, a lighter element. Many subatomic particles, such as muons and neutrons, are unstable and decay quickly into other particles. See more at decay.

  2. Relating to a chemical compound that readily decomposes or changes into other compounds or into elements.

  3. Relating to an atom or chemical element that is likely to share electrons; reactive.

  4. Characterized by uncertain or inadequate response to treatment and the potential for unfavorable outcome, as the status of a medical condition or disease.


The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Example sentences
The two approaches, visual studies and art history, create a kind of unstable
  oil-and-water mixture in academic writing.
Sweet wines are alcoholic, fattening and unstable when transported.
These different forms of an element-called isotopes-are inherently stable or
  unstable.
Such abnormal hemoglobins often do not transport oxygen efficiently and may
  also be unstable.
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