Source : Webster's Revised Unabridged Dictionary (1913)

Amplitude \Am"pli*tude\, n. [L. amplitudo, fr. amplus: cf. F.
   amplitude. See {Ample}.]
   1. State of being ample; extent of surface or space;
      largeness of dimensions; size.

            The cathedral of Lincoln . . . is a magnificent
            structure, proportionable to the amplitude of the
            diocese.                              --Fuller.

   2. Largeness, in a figurative sense; breadth; abundance;
      fullness.
      (a) Of extent of capacity or intellectual powers.
          ``Amplitude of mind.'' --Milton. ``Amplitude of
          comprehension.'' --Macaulay.
      (b) Of extent of means or resources. ``Amplitude of
          reward.'' --Bacon.

   3. (Astron.)
      (a) The arc of the horizon between the true east or west
          point and the center of the sun, or a star, at its
          rising or setting. At the rising, the amplitude is
          eastern or ortive: at the setting, it is western,
          occiduous, or occasive. It is also northern or
          southern, when north or south of the equator.
      (b) The arc of the horizon between the true east or west
          point and the foot of the vertical circle passing
          through any star or object.

   4. (Gun.) The horizontal line which measures the distance to
      which a projectile is thrown; the range.

   5. (Physics) The extent of a movement measured from the
      starting point or position of equilibrium; -- applied
      especially to vibratory movements.

   6. (math.) An angle upon which the value of some function
      depends; -- a term used more especially in connection with
      elliptic functions.

   {Magnetic amplitude}, the angular distance of a heavenly
      body, when on the horizon, from the magnetic east or west
      point as indicated by the compass. The difference between
      the magnetic and the true or astronomical amplitude (see 3
      above) is the ``variation of the compass.''

Source : WordNet®

amplitude
     n 1: (physics) the maximum displacement of a periodic wave
     2: the property of copious abundance [syn: {bountifulness}, {bounty}]
     3: greatness of magnitude