adj
Common
unstable
uhn-STAY-buhl
Unstable (adj) means Likely to shift, collapse, or change suddenly; not firmly fixed. Example: “The tower of boxes looked unstable, so she moved it away from the door.”
adj
1
Likely to shift, collapse, or change suddenly; not firmly fixed.
"The tower of boxes looked unstable, so she moved it away from the door."
"The ladder felt unstable, so he climbed down carefully."
"Investors worried about the unstable political situation."
2
Emotionally erratic or prone to sudden mood changes.
"She was so unstable that she laughed one minute and cried the next."
"Doctors say an unstable mood can be a sign that someone needs support."
"His unstable behaviour worried his close friends."
3
In chemistry or physics, prone to breaking down or decaying, sometimes radioactively.
"Some atoms are unstable and slowly give off radiation as they decay."
"The chemist stored the unstable liquid in a cool, sealed container."
"The compound is unstable and decomposes quickly at room temperature."
How to use unstable
Learner’s notesIn plain EnglishNot steady — physically shaky, emotionally erratic, or chemically prone to breaking down.
Common pairings
unstable ground
emotionally unstable
unstable isotope
politically unstable
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Word forms
- Third person singular
- unstables
- Past tense
- unstabled
- Comparative
- more unstable
- Superlative
- most unstable
Fill the gap
Can you complete this real example?
The tower of boxes looked _____, so she moved it away from the door.
Etymology
Came from Middle English unstable, equivalent to un- (not) and stable.
Synonyms
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Related words
Rhymes for unstable
See all rhymes for unstable →Frequently asked questions
What does “unstable” mean?
The word “unstable” means likely to shift, collapse, or change suddenly; not firmly fixed. In plain terms, not steady — physically shaky, emotionally erratic, or chemically prone to breaking down.
How do you pronounce “unstable”?
“Unstable” is pronounced uhn-STAY-buhl (/ʌnˈsteɪ.bəl/ in IPA).
How do you use “unstable” in a sentence?
Here is “unstable” used in a sentence: “The ladder felt unstable, so he climbed down carefully.”
What is another word for “unstable”?
Words with a similar meaning to “unstable” include unsteady and wobbly.
What is the opposite of “unstable”?
The opposite of “unstable” — its antonyms — is stable.
What part of speech is “unstable”?
“Unstable” is an adjective.
Is “unstable” a common word?
“Unstable” is a fairly common word in modern English.
How many meanings does “unstable” have?
“Unstable” has 3 distinct senses listed in this dictionary. The most common is: likely to shift, collapse, or change suddenly; not firmly fixed.
What is the difference between "unstable" and "unsteady"?
"Unstable" means likely to shift, collapse, or change suddenly and can apply to structures, situations, emotions, or substances. "Unsteady" is narrower and usually describes shaky physical movement or balance, as in unsteady hands or an unsteady walk.
What is the difference between "unstable" and "volatile"?
Both suggest a lack of steadiness, but "unstable" means prone to shifting, collapsing, or breaking down, while "volatile" emphasizes rapid, unpredictable, and often explosive change. A market can be unstable over time and volatile from moment to moment.
When is "unstable" used to describe a person?
When applied to a person, "unstable" usually means emotionally erratic or prone to sudden mood changes. This use can sound clinical or judgmental, so it is often softened in everyday speech to phrases like "going through a hard time."
How is "unstable" used in chemistry and physics?
In chemistry and physics, "unstable" describes a substance or particle prone to breaking down or decaying, sometimes radioactively. An unstable element or compound tends to react or transform readily rather than staying unchanged.
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