English Reference

Word

inertia

Phoneticsin·er·tia

US/ˌɪˈnɝʃə/

UK/ɪnˈɜːʃɐ/

Definitions

01physics

C1 · Science

n. the way an object keeps moving in the same direction unless something stops it.

n. the physical property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

“The car kept sliding on the ice because of its own inertia.”

“The spacecraft utilized its own inertia to maintain a constant velocity through the vacuum of space without further fuel consumption.”

Technical

Usage

Uncountable in this scientific context.

02unwillingness to change

C1

n. a feeling of not wanting to move, act, or change a situation.

n. a tendency to remain unchanged or a lack of motivation to initiate action.

“Bureaucratic inertia made it very difficult to change the old company rules.”

“The government's failure to address the housing crisis was largely attributed to political inertia and a fear of upsetting the status quo.”

Academic

Usage

Often used with 'bureaucratic', 'political', or 'institutional'.

Synonyms

03medical

C2 · Medicine

n. a condition where a part of the body, like the uterus during birth, stops working as hard as it should.

n. a state of sluggishness or lack of activity in an organ, specifically referring to the failure of the uterus to contract sufficiently during childbirth.

“The doctors were concerned about uterine inertia during the long labor.”

“Primary uterine inertia may occur if the muscle wall is overstretched, leading to a failure in the progression of the first stage of labor.”

Technical

Usage

Usually uncountable; typically appears in the phrase 'uterine inertia'.

Synonyms

sluggishnessinactivity

Real-World Examples

“Such comments also indicate an inertia problem of language change: Many people won’t use alternative terms like plug and socket until others in their professional community do.”
The Conversation · 25 Aug 2026
“Camilleri is a sharp and physically lively actor, bringing levity and perspective to a tale of gothic inertia.”
The Guardian · 29 Aug 2026

Etymology

From Latin inertia (“lack of art or skill, inactivity, indolence”), from iners (“unskilled, inactive”), from in- (“without, not”) + ars (“skill, art”). Something close to the modern physics sense was first used in New Latin by Johannes Kepler.

Etymology adapted from Wiktionary, available under CC BY-SA 4.0.

Word family

inertiaNouninertialAdjective

Domains

MedicinePhysics

This entry

Level
C1 · Advanced
Frequency
Occasional
Updated

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English Reference