Definition

1. Adjective:
   • Liable to change or fail; not firmly fixed or steady: Describes something that is not secure, constant, or reliable, and is likely to change, shift, or collapse.
   • Prone to emotional or psychological change; not balanced: Describes a person's mental or emotional state that is erratic, unpredictable, or not steady.
   • Chemically highly reactive; liable to decompose or change form easily: Describes a substance that can undergo a sudden or violent change.

Usage and Examples

• Describing a physical or situational lack of stability:
  • The old chair was unstable and wobbled dangerously.
  • The country entered an unstable period after the revolution.
• Describing emotional or mental variability:
  • He was in an unstable state of mind after the accident.
  • Her unstable moods made it difficult to work with her.
• Describing a reactive chemical compound:
  • The chemist handled the unstable explosive with extreme care.

Advanced Usage and Nuances

• "Unstable equilibrium": A state of balance that is easily disturbed, often used in physics and engineering.
  • The ball resting on the hilltop is in a state of unstable equilibrium.
• Used to describe abstract systems or conditions that are volatile and prone to disruption.
  • The merger created an unstable alliance between the two companies.

Variants and Related Words

• Instability (n): The state of being unstable.
  • Political instability can deter foreign investment.
• Unstably (adv): In an unstable manner.
  • The structure was built unstably and soon collapsed.

Synonyms

• Precarious: Not securely held or in position; dangerously likely to fall or collapse.
• Volatile: Liable to change rapidly and unpredictably, especially for the worse.
• Unsteady: Not firmly fixed, supported, or balanced.

Antonyms

• Stable: Not likely to change or fail; firmly established.
• Steady: Firmly fixed, supported, or balanced; regular and even.
• Constant: Occurring continuously over a period of time.

Related Phrases and Idioms

• On unstable ground: In a risky, uncertain, or insecure position.
  • His argument is on unstable ground due to the lack of evidence.
• Unstable as water: Extremely changeable or inconstant (a biblical allusion).
  • His loyalties were unstable as water.

Adjective

1. subject to change; variable
   • a fluid situation fraught with uncertainty
   • everything was unstable following the coup
2. disposed to psychological variability
   • his rather unstable religious convictions
3. suffering from severe mental illness
   • of unsound mind
4. affording no ease or reassurance
   • a precarious truce
5. highly or violently reactive
   • sensitive and highly unstable compounds
6. lacking stability or fixity or firmness
   • unstable political conditions
   • the tower proved to be unstable in the high wind
   • an unstable world economy