inertial Definition

inertia
noun

1. physics.
The tendency of an object to remain at rest, or to continue to move in the same direction at constant speed, unless it is acted on by an external force.
2. The state of not wanting to move, act or think; indolence; sluggishness.

Thesaurus: inactivity, stillness, deadness, lethargy, indolence, idleness, sluggishness, torpor, laziness; Antonym: activity, liveliness.

Derivative: inertial
adj

Etymology: 18c: from Latin iners (see inert).