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Dictionary.com Unabridged (v 1.1) - Cite This Source - Share This

un·sta·ble

Audio Help [uhn-stey-buh

–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; ME; see un-¹, stable²

]

—Related forms

un·sta·ble·ness, noun

un·sta·bly, adverb

—Synonyms 2. precarious. 2, 3. See unsettled. 3. vacillating.

Dictionary.com Unabridged (v 1.1)
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.

Encyclopædia Britannica, Inc.
Unstable

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American Heritage Dictionary - Cite This Source - Share This

un·sta·ble Audio Help (ŭn-stā'bəl) Pronunciation Key
adj. un·sta·bler, un·sta·blest

1. Tending strongly to change: unstable weather.
2. Not constant; fluctuating: unstable vital signs.
3. Fickle.
4. Lacking control of one's emotions; marked by unpredictable behavior.
5. Decomposing readily.
6. Highly or violently reactive.
7. Decaying with relatively short lifetime. Used of subatomic particles.
8. Radioactive.
1. Fickle.
2. Lacking control of one's emotions; marked by unpredictable behavior.
3. Decomposing readily.
4. Highly or violently reactive.
5. Decaying with relatively short lifetime. Used of subatomic particles.
6. Radioactive.
Not firmly placed; unsteady: an unstable ladder.
Chemistry
1. Decomposing readily.
2. Highly or violently reactive.
3. Decaying with relatively short lifetime. Used of subatomic particles.
4. Radioactive.
Physics
1. Decaying with relatively short lifetime. Used of subatomic particles.
2. Radioactive.

un·sta'ble·ness n., un·sta'bly adv.

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The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2006 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.

Online Etymology Dictionary - Cite This Source - Share This
unstable

c.1225, "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 c.1290.

WordNet - Cite This Source - Share This

unstable
adjective
1.	lacking stability or fixity or firmness; "unstable political conditions"; "the tower proved to be unstable in the high wind"; "an unstable world economy" [ant: stable]
2.	highly or violently reactive; "sensitive and highly unstable compounds"
3.	affording no ease or reassurance; "a precarious truce" [syn: precarious]
4.	suffering from severe mental illness; "of unsound mind" [syn: mentally ill]
5.	disposed to psychological variability; "his rather unstable religious convictions"
6.	subject to change; variable; "a fluid situation fraught with uncertainty"; "everything was unstable following the coup" [syn: fluid]

The American Heritage Science Dictionary - Cite This Source - Share This

unstable Audio Help (ŭn-stā'bəl) Pronunciation Key

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.

Merriam-Webster's Medical Dictionary - Cite This Source - Share This

Main Entry: un·sta·ble
Pronunciation: -'stA-b&l
Function: adjective
: not stable: as a : characterized by frequent or unpredictable changes <a patient in unstable condition> b : readily changing (as by decomposing) in chemical composition or biological activity c : characterized by inability to control the emotions

Webster's Revised Unabridged Dictionary - Cite This Source - Share This

Unstable

In*sta"ble\, a. [L. instabilis: cf. F. instable. See In- not, and Stable, a., and cf. Unstable.] Not stable; not standing fast or firm; unstable; prone to change or recede from a purpose; mutable; inconstant.

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