Meaning & use
unstable
Likely to change, fail, or collapse suddenly; not firmly fixed or balanced.
See it in a sentence
The old bridge was declared unstable after inspectors found cracks in its main supports.
Her mood had been unstable all week, swinging from cheerful to tearful without warning.
A note on using this word
Unstable can describe physical structures, emotions, chemical compounds, or political situations; the shared idea is a lack of secure balance.
Words with a similar meaning
Choose a synonym to suit the sentence. Meanings can overlap without being identical.
Words with an opposite meaning
stablesteady
Another way to use it
2. adjective
Relating to a chemical substance that decomposes or reacts easily.
The compound was too unstable to store at room temperature and had to be refrigerated.
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