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unstable

[uhn-stey-buh l]
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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.
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Origin of unstable

Middle English word dating back to 1175–1225; see origin at un-1, stable2
Related formsun·sta·ble·ness, nounun·sta·bly, adverb

Synonyms

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2. precarious. 2, 3. See unsettled. 3. vacillating.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for unstably

unstable

adjective
  1. lacking stability, fixity, or firmness
  2. disposed to temperamental, emotional, or psychological variability
  3. (of a chemical compound) readily decomposing
  4. physics
    1. (of an elementary particle) having a very short lifetime
    2. spontaneously decomposing by nuclear decay; radioactivean unstable nuclide
  5. electronics (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation
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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 unstably

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.

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Online Etymology Dictionary, © 2010 Douglas Harper

unstably in Science

unstable

[ŭn-stābəl]
  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.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.