unstable
unstable — adjective
1. not firmly fixed, positioned, or balanced, so that something or someone is likel
not firmly fixed, positioned, or balanced, so that something or someone is likely to move, fall, or break.
The old wooden chair wobbled because one of its legs was unstable.
collocation: unstable + leg / structure / surface
Niran placed the vase on an unstable shelf, and it crashed to the floor.
After the earthquake, engineers declared the bridge unstable and closed it.
Liang held the ladder for Beatriz because the ground beneath it was uneven and unstable.
A pile of loose stones made the path unstable for hikers carrying heavy bags.
- unsteady
less formal, often used for movement or gait rather than fixed position
- wobbly
informal; describes something that moves from side to side when touched
- precarious
more formal; suggests danger of collapsing or falling at any moment
- rickety
informal; describes old, poorly made structures likely to break
用法筆記
Frequently used for physical objects (furniture, buildings, ground surfaces) and extended to abstract things such as political systems or economic conditions.
常見錯誤
2. describes a person whose emotions, behaviour, or state of mind changes suddenly
describes a person whose emotions, behaviour, or state of mind changes suddenly and extremely, often because of a mental health condition.
After losing her job, Noa became emotionally unstable and struggled to sleep.
collocation: emotionally / mentally unstable
The court ordered a psychological evaluation to determine whether the defendant was mentally unstable.
Selim's friends noticed he had become increasingly unstable and urged him to see a therapist.
Maeve worried that her brother's unstable behaviour might get him into trouble at school.
The report described the patient as psychologically unstable and in need of long-term care.
- volatile
suggests sudden, explosive mood swings; slightly more formal
- unbalanced
less clinical; suggests a lack of mental equilibrium
- erratic
focuses on unpredictable behaviour rather than internal state
- stable
the opposite in mental/emotional contexts
- well-adjusted
positive informal term for healthy mental state
用法筆記
Often used in clinical, legal, or journalistic contexts. Avoid using this term casually or as an insult in everyday speech because it carries a strong negative judgement about a person's mental health.
常見錯誤
3. describes a chemical substance or compound that readily changes its composition,
describes a chemical substance or compound that readily changes its composition, decomposes, or reacts with other substances, often in a dangerous or unpredictable way.
The lab assistant stored the unstable compound in a special container to prevent an explosion.
collocation: unstable + compound / chemical / substance
Jin warned the trainees that the mixture becomes unstable if heated too quickly.
Some radioactive elements are naturally unstable and break down into other elements over time.
Élise checked the safety data sheet before handling the unstable reagent in the laboratory.
- reactive
emphasises a tendency to react with other substances
- volatile
specifically suggests rapid evaporation or dangerous reaction at room temperature
- decomposable
technical; focuses on breaking down into simpler components
用法筆記
Mostly used in scientific or technical writing. In everyday language, sense 1 or 2 is preferred. The term does NOT describe emotional states when used in a chemistry context.