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

/ ŭn-stā′bəl /

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.

Derived Forms

• unˈstably, adverb
• unˈstableness, noun

Other Words From

• un·stable·ness noun
• un·stably adverb

Word History and Origins

Origin of unstable¹

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

Synonym Study

See unsettled.

Example Sentences

They discovered that some of the pre-fusion F proteins appeared to be unstable and sometimes converted to an open form, or even less desirable, a post-fusion form.

From Science Daily

“I like Trump, but he’s unstable. Who knows what he might do?” says the 74-year-old pensioner, whose name has been withheld.

From BBC

Many players said the game's frame rate - which governs the smoothness of on-screen animations - was unstable.

From BBC

The flooding in Valencia was caused by a Dana phenomenon - when warm, moist air meets cold air, creating an unstable weather system.

From BBC

Antioxidants neutralize free radicals, which are unstable molecules that harm our cells.

From Salon

Related Words

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