from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. Physics The tendency of a body to resist acceleration; the tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force.
  • n. Resistance or disinclination to motion, action, or change: the inertia of an entrenched bureaucracy.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The property of a body that resists any change to its uniform motion; equivalent to its mass.
  • n. In a person, unwillingness to take action.

from the GNU version of the Collaborative International Dictionary of English

  • n. That property of matter by which it tends when at rest to remain so, and when in motion to continue in motion, and in the same straight line or direction, unless acted on by some external force; -- sometimes called vis inertiæ. The inertia of a body is proportional to its mass.
  • n. Inertness; indisposition to motion, exertion, or action; lack of energy; sluggishness.
  • n. Lack of activity; sluggishness; -- said especially of the uterus, when, in labor, its contractions have nearly or wholly ceased.

from The Century Dictionary and Cyclopedia

  • n. Lack of activity; sluggishness; passiveness; inertness.
  • n. In physics, that property of matter by virtue of which it retains its state of rest or of uniform rectilinear motion so long as no foreign cause changes that state. Also called vis inertiæ (force of inertia).
  • n. In medicine, want of activity; sluggishness: a term especially applied to the condition of the uterus when it does not contract properly in parturition.
  • n. With regard to a plane or point, the sum of the elements of mass each multiplied by the square of its distance from the given plane or point.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. (physics) the tendency of a body to maintain its state of rest or uniform motion unless acted upon by an external force
  • n. a disposition to remain inactive or inert


Latin, idleness, from iners, inert-, inert; see inert.
(American Heritage® Dictionary of the English Language, Fourth Edition)
From Latin inertia ("lack of art or skill, inactivity, indolence"), from iners ("unskilled, inactive"), from in- ("without, not") + ars ("skill, art"). (Wiktionary)



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