Source : Webster's Revised Unabridged Dictionary (1913)

Energy \En"er*gy\, n.; pl. {Energies}. [F. ['e]nergie, LL.
   energia, fr. Gr.?, fr. ? active; ? in + ? work. See {In}, and
   {Work}.]
   1. Internal or inherent power; capacity of acting, operating,
      or producing an effect, whether exerted or not; as, men
      possessing energies may suffer them to lie inactive.

            The great energies of nature are known to us only by
            their effects.                        --Paley.

   2. Power efficiently and forcibly exerted; vigorous or
      effectual operation; as, the energy of a magistrate.

   3. Strength of expression; force of utterance; power to
      impress the mind and arouse the feelings; life; spirit; --
      said of speech, language, words, style; as, a style full
      of energy.

   4. (Physics) Capacity for performing work.

   Note: The kinetic energy of a body is the energy it has in
         virtue of being in motion. It is measured by one half
         of the product of the mass of each element of the body
         multiplied by the square of the velocity of the
         element, relative to some given body or point. The
         available kinetic energy of a material system
         unconnected with any other system is that energy which
         is due to the motions of the parts of the system
         relative to its center of mass. The potential energy of
         a body or system is that energy which is not kinetic;
         -- energy due to configuration. Kinetic energy is
         sometimes called actual energy. Kinetic energy is
         exemplified in the vis viva of moving bodies, in heat,
         electric currents, etc.; potential energy, in a bent
         spring, or a body suspended a given distance above the
         earth and acted on by gravity.

Source : WordNet®

energy
     n 1: (physics) the capacity of a physical system to do work; the
          units of energy are joules or ergs; "energy can take a
          wide variety of forms"
     2: an exertion of force; "he plays tennis with great energy"
        [syn: {vigor}, {vigour}]
     3: enterprising or ambitious drive; "Europeans often laugh at
        American energy" [syn: {push}, {get-up-and-go}]
     4: an imaginative lively style (especially style of writing);
        "his writing conveys great energy" [syn: {vigor}, {vigour},
         {vim}]
     5: a healthy capacity for vigorous activity; "jogging works off
        my excess energy"; "he seemed full of vim and vigor" [syn:
         {vim}, {vitality}]
     6: the federal department responsible for maintaining a
        national energy policy of the United States; created in
        1977 [syn: {Department of Energy}, {Energy Department}, {DOE}]