inertia

American  

[in-ur-shuh, ih-nur-] / ɪnˈɜr ʃə, ɪˈnɜr- /

noun

1. inertness, especially with regard to effort, motion, action, and the like; inactivity; sluggishness.

   Synonyms:

   laziness, inaction, torpor

2. Physics.

   1. the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force.

   2. an analogous property of a force.

      electric inertia.

3. Medicine/Medical. lack of activity, especially as applied to a uterus during childbirth when its contractions have decreased or stopped.

---

inertia British  

/ ɪnˈɜːʃə, -ʃɪə /

noun

1. the state of being inert; disinclination to move or act

2. physics

   1. the tendency of a body to preserve its state of rest or uniform motion unless acted upon by an external force

   2. an analogous property of other physical quantities that resist change

      thermal inertia

---

inertia Scientific  

/ ĭ-nûr′shə /

1. The resistance of a body to changes in its momentum. Because of inertia, a body at rest remains at rest, and a body in motion continues moving in a straight line and at a constant speed, unless a force is applied to it. Mass can be considered a measure of a body's inertia.

2. See more at Newton's laws of motion See also mass

---

inertia Cultural  

1. In physics, the tendency for objects at rest to remain at rest, and for objects in uniform motion to continue in motion in a straight line, unless acted on by an outside force. (See Newton's laws of motion.)

---

Other Word Forms

• inertial adjective
• noninertial adjective

Etymology

Origin of inertia

First recorded in 1705–15; from Latin: “lack of skill, slothfulness”; inert, -ia

Example Sentences

The major human spaceflight programs are supertankers, with tremendous inertia.

From Slate • Mar. 13, 2026

Those details would come amid the current inertia of the “no hire, no fire” job market, and as analysts watch for the impacts of AI on headcount.

From MarketWatch • Jan. 12, 2026

After a customary bout of second half inertia, the Eagles managed to retake the lead with three minutes left.

From The Wall Street Journal • Jan. 12, 2026

At everyday scales, motion is shaped by forces such as gravity and inertia, which depend on an object's volume.

From Science Daily • Jan. 6, 2026

His very smell like that of coming winter, a tomb, the heavy inertia of time.

From "All the Light We Cannot See" by Anthony Doerr

Related Words

• apathy
• laziness
• paralysis
• passivity
• sluggishness