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

"My father, an uncle and I came before the rest of the family by sea. The small ship was overloaded and very unstable. All the time we feared the vessel might capsize."

Read more on Barron's

And scientists say a warm, wet Tibet could mean unstable weather and frequent snowstorms and blizzards.

Read more on BBC

Three Hills didn’t invest much in Italy until recently, for fear of spooking investors put off by the country’s sluggish economy and unstable politics.

Read more on The Wall Street Journal

But "the running of the government will be extremely unstable", he warned, "with everything decided in a form of cooperation from outside the government".

Read more on Barron's

The Philippines, which sits on the geologically unstable "Ring of Fire", has been reeling from a string of devastating natural disasters.

Read more on BBC

Related Words

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