unstable

adjective

un·​sta·​ble ˌən-ˈstā-bəl 

: not stable : not firm or fixed : not constant: such as

a

: not steady in action or movement : irregular

an unstable pulse

b

: wavering in purpose or intent : vacillating

c

: lacking steadiness : apt to move, sway, or fall

an unstable tower

d(1)

: liable to change or alteration

an unstable economy

unstable weather

(2)

: readily changing (as by decomposing) in chemical or physical composition or in biological activity

e

: characterized by lack of emotional control

unstableness noun

unstably

ˌən-ˈstā-b(ə-)lē 

adverb

Synonyms

• unbalanced
• unsteady

Choose the Right Synonym for unstable

inconstant, fickle, capricious, mercurial, unstable mean lacking firmness or steadiness (as in purpose or devotion).

inconstant implies an incapacity for steadiness and an inherent tendency to change.

an inconstant friend

fickle suggests unreliability because of perverse changeability and incapacity for steadfastness.

performers discover how fickle fans can be

capricious suggests motivation by sudden whim or fancy and stresses unpredictability.

an utterly capricious critic

mercurial implies a rapid changeability in mood.

made anxious by her boss's mercurial temperament

unstable implies an incapacity for remaining in a fixed position or steady course and applies especially to a lack of emotional balance.

too unstable to hold a job

Examples of unstable in a Sentence

an unstable nuclear reactor core

the minute we put the books down on the unstable desk, the whole stack went crashing to the floor

Recent Examples on the Web

The court paperwork from Del Mar’s restraining order lays bare the probable motive, depicting Barry as unstable and increasingly erratic. —Nate Gartrell, The Mercury News, 17 Apr. 2024

The storms will begin to settle down around sunset — 8:25 p.m. on Friday — Wojcik said, because the heat from the sun helps keep the atmosphere unstable and primed for thunderstorms. —Shaun Goodwin, Idaho Statesman, 12 Apr. 2024

Deforestation and human settlement fragment their habitat, while poaching and unstable politics in the region hinder conservation efforts. —Katie Liu, Discover Magazine, 11 Apr. 2024

That’s because the titular ingredient, which works a plethora of wonders for the skin, is about as unstable as a decades-old bistro table—at least, that is, when it’s dissolved in water. —Justin Fenner, Robb Report, 2 Apr. 2024

The culprit was the main storm clouds overhead, which became very unstable as their temperature — at around 25,000 feet — hovered at nearly minus 40 degrees Fahrenheit. —Gary Robbins, San Diego Union-Tribune, 1 Apr. 2024

The series of thunderstorms moving northward into the region, pushed along by a boundary of unstable air, will approach the I-20 corridor as early as 3-4 p.m. Monday. —David Montesino, Fort Worth Star-Telegram, 9 Apr. 2024

Russian sales are becoming ever more important for Chinese manufacturers, given unstable domestic demand in China and decreasing exports to traditional markets in the West. —Alexander Gabuev, Foreign Affairs, 9 Apr. 2024

Suddenly, anyone who had a period was seen as unstable. —Shalene Gupta, TIME, 4 Apr. 2024

Word History

First Known Use

13th century, in the meaning defined above

Phrases Containing unstable

• unstable angina

Kids Definition

unstable

adjective

un·​sta·​ble ˌən-ˈstā-bəl 

ˈən-

1

: not stable : not firm or fixed : fluctuating

unstable prices

an unstable tower

unstable weather

2

: readily changing in chemical composition or physical state or properties (as by breaking down into parts)

an unstable atomic nucleus

Medical Definition

unstable

adjective

un·​sta·​ble -ˈstā-bəl 

: not stable: as

a

: characterized by frequent or unpredictable changes

a patient in unstable condition

b

: readily changing (as by decomposing) in chemical composition or biological activity

unstable compounds

c

: characterized by lack of emotional control or stability