Source : Webster's Revised Unabridged Dictionary (1913)

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}.

         A period of social improvement, or of intellectual
         advancement, contains within itself a principle of
         acceleration.                            --I. Taylor.
   (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.