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definitions

unstable

[ uhn-stey-buhl ]
/ ʌnˈsteɪ bəl /
||
SEE MORE SYNONYMS FOR unstable ON THESAURUS.COM

adjective

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.

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RELATED WORDS

tricky, ambiguous, uncertain, irrational, sensitive, unsettled, insecure, shaky, weak, precarious, rocky, unpredictable, fickle, volatile, wobbly, ticklish, slippery, changeable, unsteady, erratic

Nearby words

  1. unspoiled,
  2. unspoken,
  3. unsporting,
  4. unsportsmanlike,
  5. unspotted,
  6. unstable angina,
  7. unstainable,
  8. unstained,
  9. unstalked,
  10. unstarry

Origin of unstable

Middle English word dating back to 1175–1225; see origin at un-1, stable2
SYNONYMS FOR unstable
2 precarious.
2, 3 See unsettled.
3 vacillating.
SEE MORE SYNONYMS FOR unstable ON THESAURUS.COM
Related formsun·sta·ble·ness, nounun·sta·bly, adverb
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for unstable

British Dictionary definitions for unstable

unstable

/ (ʌnˈsteɪbəl) /

adjective

lacking stability, fixity, or firmness
disposed to temperamental, emotional, or psychological variability
(of a chemical compound) readily decomposing
physics
  1. (of an elementary particle) having a very short lifetime
  2. spontaneously decomposing by nuclear decay; radioactivean unstable nuclide
electronics (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation
Derived Formsunstableness, noununstably, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for unstable

unstable

adj.

early 13c., "apt to move," from un- (1) "not" + stable (adj.). Cf. Middle High German unstabel. Meaning "liable to fall" is recorded from c.1300; sense of "fickle" is attested from late 13c. An Old English word for this was feallendlic, which might have become *fally.

Online Etymology Dictionary, © 2010 Douglas Harper

Science definitions for unstable

unstable

[ ŭn-stā′bəl ]

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.
Relating to a chemical compound that readily decomposes or changes into other compounds or into elements.
Relating to an atom or chemical element that is likely to share electrons; reactive.
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 © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.