unstable

[uhn-stey-buhl]

adjective

1. not stable; not firm or firmly fixed; unsteady.

2. liable to fall or sway.

   Synonyms: precarious

3. unsteadfast; inconstant; wavering.

   unstable convictions.

   Synonyms: vacillating

4. marked by emotional instability.

   an unstable person.

5. irregular in movement.

   an unstable heartbeat.

6. Chemistry.,  noting compounds that readily decompose or change into other compounds.

unstable

/ ʌnˈsteɪbəl /

adjective

1. lacking stability, fixity, or firmness

2. disposed to temperamental, emotional, or psychological variability

3. (of a chemical compound) readily decomposing

4. physics

   1. (of an elementary particle) having a very short lifetime

   2. spontaneously decomposing by nuclear decay; radioactive

      an unstable nuclide

5. electronics (of an electrical circuit, mechanical body, etc) having a tendency to self-oscillation

unstable

1. Liable to undergo spontaneous decay into some other form. For example, the nucleus of uranium 238 atom is unstable and changes by radioactive decay into the nucleus of thorium 234, a lighter element. Many subatomic particles, such as muons and neutrons, are unstable and decay quickly into other particles.

2. See more at decay

3. Relating to a chemical compound that readily decomposes or changes into other compounds or into elements.

4. Relating to an atom or chemical element that is likely to share electrons; reactive.

5. Characterized by uncertain or inadequate response to treatment and the potential for unfavorable outcome, as the status of a medical condition or disease.

Other Word Forms

• unstably adverb
• unstableness noun

Word History and Origins

Origin of unstable¹

First recorded in 1175–1225; Middle English; un- ¹ + stable ²

Synonym Study

See unsettled.

Example Sentences

Perched atop four active landslides, its pavement warped and cracked by constant land movement, Last Chance Grade is so unstable that it was reduced to one-way traffic for nine years straight, reopening in October 2023.

From Los Angeles Times

Meanwhile, he said, those in park housing face safety threats such as hantavirus-carrying rodents that invade living spaces, caving-in roofs and unstable decks.

From Los Angeles Times

After leaving the school at 16, he ran away to London because his home life was still unstable.

From BBC

That pattern will keep the area unstable — and likely hot — into next week, when long-range forecasts show mercury could begin falling, said Sam Zuber, a weather service meteorologist in San Diego.

From Los Angeles Times

Though not a stumble by most people’s measure, Swift doesn’t like her footing to be unstable.

From Salon

Related Words

• ambiguous 
• changeable 
• erratic 
• fickle 
• insecure 
• irrational 
• precarious 
• risky 
• rocky 
• sensitive 
• shaky 
• slippery 
• ticklish 
• tricky 
• uncertain 
• unpredictable 
• unsettled 
• unsteady 
• volatile 
• weak