*acceleration*

n. [ L. acceleratio: cf. F. accélération. ] The act of accelerating, or the state of being accelerated; increase of motion or action; as, a falling body moves toward the earth with an acceleration of velocity; -- opposed to retardation. [ 1913 Webster ]

A period of social improvement, or of intellectual advancement, contains within itself a principle of acceleration. I. Taylor. [ 1913 Webster ]

(Astr. & Physics.)
Acceleration of the moon, the increase of the moon's mean motion in its orbit, in consequence of which its period of revolution is now shorter than in ancient times. --
Acceleration and
retardation of the tides. See Priming of the tides, under Priming. --
Diurnal acceleration of the fixed stars, the amount by which their apparent diurnal motion exceeds that of the sun, in consequence of which they daily come to the meridian of any place about three minutes fifty-six seconds of solar time earlier than on the day preceding. --
Acceleration of the planets, the increasing velocity of their motion, in proceeding from the apogee to the perigee of their orbits. [ 1913 Webster ]