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
Predictably, the war has shaken up the already unstable Middle East and driven oil prices skyward.
—
Clarence Page, Chicago Tribune, 16 Mar. 2026
Abundant moisture makes for an unstable atmosphere that will cause thunderstorms to develop and that, along with the strong winds, could create tornadoes.
—Andrea Thompson, Scientific American, 16 Mar. 2026
Some calls reported that O’Connor had unstable housing or had previously used drugs.
—Caroline Zimmerman, Kansas City Star, 16 Mar. 2026
Even though the atmosphere will only be marginally unstable, that line of storms could act like a conveyor belt to help pull stronger winds down to the surface.
—Jacob Wycoff, CBS News, 15 Mar. 2026
See All Example Sentences for unstable
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Clarence Page, Chicago Tribune, 16 Mar. 2026
Abundant moisture makes for an unstable atmosphere that will cause thunderstorms to develop and that, along with the strong winds, could create tornadoes.
—Andrea Thompson, Scientific American, 16 Mar. 2026
Some calls reported that O’Connor had unstable housing or had previously used drugs.
—Caroline Zimmerman, Kansas City Star, 16 Mar. 2026
Even though the atmosphere will only be marginally unstable, that line of storms could act like a conveyor belt to help pull stronger winds down to the surface.
—Jacob Wycoff, CBS News, 15 Mar. 2026
See All Example Sentences for unstable
Cite this Entry
“Unstable.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/unstable. Accessed 19 Mar. 2026.
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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