{ ‖ } n. [ NL. anergia, fr. Gr. &unr_;- not + &unr_; work. ] Lack of energy; inactivity. -- An*er"gic a. [Webster 1913 Suppl.]

n. [ L., idleness, fr. iners idle. See Inert. ] [ 1913 Webster ]

1. (Physics) 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. [ 1913 Webster +PJC ]

2. Inertness; indisposition to motion, exertion, or action; lack of energy; sluggishness. [ 1913 Webster ]

Men . . . have immense irresolution and inertia. Carlyle. [ 1913 Webster ]

3. (Med.) Lack of activity; sluggishness; -- said especially of the uterus, when, in labor, its contractions have nearly or wholly ceased. [ 1913 Webster ]

Center of inertia. (Mech.) See under Center. [ 1913 Webster ]