inertia

Concise Oxford English Dictionary © 2008 Oxford University Press:
inertia /ɪˈnəːʃə/

▶noun

• 1 a tendency to do nothing or to remain unchanged.

• 2 Physics a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless changed by an external force.

  ■ resistance to change in some other physical property: the thermal inertia of the oceans.

– origin C18: from L., from iners, inert- (see inert).