unstable
adjective
un·sta·ble
ˌən-ˈstā-bəl 
: not stable : not firm or fixed : not constant: such as
a
: not steady in action or movement : irregular
an unstable pulse
b
: wavering in purpose or intent : vacillating
c
: lacking steadiness : apt to move, sway, or fall
an unstable tower
d(1)
: liable to change or alteration
an unstable economy
unstable weather
(2)
: readily changing (as by decomposing) in chemical or physical composition or in biological activity
e
: characterized by lack of emotional control
unstableness
noun
Examples of unstable in a Sentence
an unstable nuclear reactor core
the minute we put the books down on the unstable desk, the whole stack went crashing to the floor
Recent Examples on the Web
Rigid robots are prone to damage in unstable, cramped environments and are expensive to repair.
—
Kurt Knutsson, FOXNews.com, 28 Apr. 2025
Remember: Antioxidants can slow aging and prevent skin damage caused by unstable molecules called free radicals.
—Danielle Jackson, Glamour, 28 Apr. 2025
Polyphenols neutralize unstable, harmful molecules (free radicals) in the body that contribute to inflammation and cell damage.
—Amy Brownstein, Ms, Rdn, Verywell Health, 25 Apr. 2025
The twinkling effect is caused by the unstable state of the air through which a star's light must pass to reach our eyes.
—Joe Rao, Space.com, 25 Apr. 2025
See All Example Sentences for unstable
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Kurt Knutsson, FOXNews.com, 28 Apr. 2025
Remember: Antioxidants can slow aging and prevent skin damage caused by unstable molecules called free radicals.
—Danielle Jackson, Glamour, 28 Apr. 2025
Polyphenols neutralize unstable, harmful molecules (free radicals) in the body that contribute to inflammation and cell damage.
—Amy Brownstein, Ms, Rdn, Verywell Health, 25 Apr. 2025
The twinkling effect is caused by the unstable state of the air through which a star's light must pass to reach our eyes.
—Joe Rao, Space.com, 25 Apr. 2025
See All Example Sentences for unstable
Cite this Entry
“Unstable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unstable. Accessed 1 May. 2025.
Copy CitationKids Definition
unstable
adjective
un·sta·ble
ˌən-ˈstā-bəl
ˈən-
1
: not stable : not firm or fixed : fluctuating
unstable prices
an unstable tower
unstable weather
2
: readily changing in chemical composition or physical state or properties (as by breaking down into parts)
an unstable atomic nucleus
Medical Definition
unstable
adjective
un·sta·ble
-ˈstā-bəl
: 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
unstable compounds
c
: characterized by lack of emotional control or stability
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