The Collaborative International Dictionary of English v.0.48:

Conservation \Con`ser*va"tion\, n. [L. conservatio: cf. F.
   conservation.]
   The act of preserving, guarding, or protecting; the keeping
   (of a thing) in a safe or entire state; preservation.
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         A step necessary for the conservation of Protestantism.
                                                  --Hallam.
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         A state without the means of some change is without the
         means of its conservation.               --Burke.
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   Conservation of areas (Astron.), the principle that the
      radius vector drawn from a planet to the sun sweeps over
      equal areas in equal times.

   Conservation of energy, or Conservation of force (Mech.),
      the principle that the total energy of any material system
      is a quantity which can neither be increased nor
      diminished by any action between the parts of the system,
      though it may be transformed into any of the forms of
      which energy is susceptible. --Clerk Maxwell.
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The Collaborative International Dictionary of English v.0.48:

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.
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            The great energies of nature are known to us only by
            their effects.                        --Paley.
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   2. Power efficiently and forcibly exerted; vigorous or
      effectual operation; as, the energy of a magistrate.
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   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.
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   4. (Physics) Capacity for performing work.
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   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.
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   Accumulation, Conservation, Correlation, & Degradation
   of energy, etc. (Physics) See under Accumulation,
      Conservation, Correlation, etc.

   Syn: Force; power; potency; vigor; strength; spirit;
        efficiency; resolution.
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WordNet (r) 3.0 (2006):

conservation
    n 1: an occurrence of improvement by virtue of preventing loss
         or injury or other change [syn: conservation,
         preservation]
    2: the preservation and careful management of the environment
       and of natural resources
    3: (physics) the maintenance of a certain quantities unchanged
       during chemical reactions or physical transformations

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "conservation":
   attention, care, cold storage, conservancy, conservationism,
   control, custody, dead storage, directing, dry storage, economy,
   environmental conservation, forest conservation, forest management,
   governing, guardianship, husbandry, keeping, maintenance,
   management, managing, preserval, preservation, protection,
   safeguarding, safekeeping, salvage, salvation, saving, shelf-room,
   soil conservation, storage, storage space, stowage,
   stream conservation, supervising, supervision, support,
   sustentation, upkeep, warehousing, water conservation,
   wetlands conservation, wildlife conservation