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

Physics .

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.

an analogous property of a force

electric inertia.

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

noun

activity , animation , life , liveliness , moving

noun

apathy , deadness , drowsiness , dullness , idleness , immobility , immobilization , inactivity , indolence , languor , lassitude , laziness , lethargy , listlessness , oscitancy , paralysis , passivity , sloth , sluggishness , stillness , stupor , torpidity , torpor , unresponsiveness , indisposition , inertness , quiescence , sleep , vis inertiae