unstable
Americanadjective
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not stable; not firm or firmly fixed; unsteady.
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liable to fall or sway.
- Synonyms:
- precarious
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unsteadfast; inconstant; wavering.
unstable convictions.
- Synonyms:
- vacillating
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marked by emotional instability.
an unstable person.
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irregular in movement.
an unstable heartbeat.
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Chemistry. noting compounds that readily decompose or change into other compounds.
adjective
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lacking stability, fixity, or firmness
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disposed to temperamental, emotional, or psychological variability
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(of a chemical compound) readily decomposing
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physics
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(of an elementary particle) having a very short lifetime
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spontaneously decomposing by nuclear decay; radioactive
an unstable nuclide
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electronics (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation
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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.
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See more at decay
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Relating to a chemical compound that readily decomposes or changes into other compounds or into elements.
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Relating to an atom or chemical element that is likely to share electrons; reactive.
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Characterized by uncertain or inadequate response to treatment and the potential for unfavorable outcome, as the status of a medical condition or disease.
Related Words
See unsettled.
Other Word Forms
- unstableness noun
- unstably adverb
Etymology
Origin of unstable
First recorded in 1175–1225; Middle English; un- 1 + stable 2
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
Researchers found that Latino students faced myriad challenges, including immigration issues, English proficiency and unstable housing that is linked to their parents’ employment status.
From Los Angeles Times • Apr. 1, 2026
But Franziska Brantner from Germany's opposition Green Party said returning to Syria was not an option for many, because of the lack of infrastructure and the unstable security situation there.
From BBC • Mar. 30, 2026
Near this point, the system becomes highly unstable, and water rapidly shifts between the two liquid states or mixtures of them.
From Science Daily • Mar. 29, 2026
That would relieve our partners in the Indo-Pacific region from reliance on dangerously unstable and vulnerable sources in the Middle East.
From The Wall Street Journal • Mar. 20, 2026
Can you imagine a beast so mean, unstable, and stinky that even pirates had kicked him off their ship?
From "The Many Assassinations of Samir, the Seller of Dreams" by Daniel Nayeri
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
