Dictionary.net

A f. which, acting upon a moving body, produces an acceleration of its motion; in particular, a f. of such degree as to produce upon the unit of mass a definite acceleration of velocity in the unit of time. The accelerating f. is measured by the acceleration of velocity thus produced. Any f. which acts continuously is an accelerating f.

[L.] Force considered simply with reference to the rate at which it increases the velocity of a moving body ; called also the accelerating quantity, the accelerative effect, and sometimes merely the acceleration of the force.