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The Collaborative International Dictionary of English v.0.48 (gcide)

Acceleration \Ac*cel`er*a"tion\, n. [L. acceleratio: cf. F.
acc['e]l['e]ration.]
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]