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
When strong lift, abundant moisture and cold, unstable air come together in the same place, the rare conditions for thundersnow can form.
—
Brandi D. Addison, USA Today, 23 Feb. 2026
Bharat Mandapam, the main venue for speakers and panels, apparently has unstable reception at the best of times, let alone when filled with hundreds of delegates.
—Beatrice Nolan, Fortune, 23 Feb. 2026
But the unstable snowpack, high winds and whiteout conditions made search-and-recovery efforts too perilous, prompting first responders to leave behind the bodies of deceased skiers and suspend operations on Wednesday and Thursday.
—Tony Briscoe, Los Angeles Times, 22 Feb. 2026
In some parts of France, however, Bornet expects the danger to persist for several weeks while the snow is still unstable.
—Issy Ronald, CNN Money, 22 Feb. 2026
See All Example Sentences for unstable
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Brandi D. Addison, USA Today, 23 Feb. 2026
Bharat Mandapam, the main venue for speakers and panels, apparently has unstable reception at the best of times, let alone when filled with hundreds of delegates.
—Beatrice Nolan, Fortune, 23 Feb. 2026
But the unstable snowpack, high winds and whiteout conditions made search-and-recovery efforts too perilous, prompting first responders to leave behind the bodies of deceased skiers and suspend operations on Wednesday and Thursday.
—Tony Briscoe, Los Angeles Times, 22 Feb. 2026
In some parts of France, however, Bornet expects the danger to persist for several weeks while the snow is still unstable.
—Issy Ronald, CNN Money, 22 Feb. 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 26 Feb. 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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