un stablest


not stable; not firm or firmly fixed; unsteady.
liable to fall or sway.
unsteadfast; inconstant; wavering: unstable convictions.
marked by emotional instability: an unstable person.
irregular in movement: an unstable heartbeat.
Chemistry. noting compounds that readily decompose or change into other compounds.

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

unstableness, noun
unstably, adverb

2. precarious. 2, 3. See unsettled. 3. vacillating.
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
unstable (ʌnˈsteɪbəl)
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

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

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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