inertia

noun

in·​er·​tia i-ˈnər-shə 

-shē-ə

1

a

: a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force

b

: an analogous property of other physical quantities (such as electricity)

2

: indisposition to motion, exertion, or change : inertness

inertial

i-ˈnər-shəl 

-shē-əl

adjective

inertially

i-ˈnər-sh(ə-)lē 

adverb

Did you know?

Inertia is the inherent property of a body that makes it oppose any force that would cause a change in its motion. A body at rest and a body in motion both oppose forces that might cause acceleration. The inertia of a body can be measured by its mass, which governs its resistance to the action of a force, or by its moment of inertia about a specified axis, which measures its resistance to the action of a torque about the same axis.

Synonyms

• laziness
• idleness

Examples of inertia in a Sentence

He blames governmental inertia for the holdup.

After 10 years in an unsatisfying job she overcame her inertia and went back to school.

Recent Examples on the Web

American inertia has become a global liability. —John Wihbey, Time, 20 Oct. 2025

More modern power resources, like wind, solar, and batteries, don't involve inertia, because they are digitally controlled. —Julia Simon, NPR, 8 Oct. 2025

The inertia continues despite economic and regulatory headwinds across the world that threaten to impact sales and product strategies. —Eileen Falkenberg-Hull, MSNBC Newsweek, 7 Oct. 2025

And by the inertia of ownership. —David Aldridge, New York Times, 2 Oct. 2025

Word History

Etymology

New Latin, from Latin, lack of skill, from inert-, iners

First Known Use

1713, in the meaning defined at sense 1a

Phrases Containing inertia

• moment of inertia

Kids Definition

inertia

noun

in·​er·​tia in-ˈər-shə 

-shē-ə

1

: a property of matter by which it remains at rest or in unchanging motion unless acted on by some external force

2

: a tendency not to move or change

inertial

-shəl 

adjective

Medical Definition

inertia

noun

in·​er·​tia in-ˈər-shə, -shē-ə 

1

a

: a property of matter by which it remains at rest or in uniform motion in the same straight line unless acted upon by some external force

b

: an analogous property of other physical quantities (as electricity)

2

: lack of activity or movement

—used especially of the uterus in labor when its contractions are weak or irregular