The Collaborative International Dictionary of English v.0.48:

Reduce \Re*duce"\ (r[-e]*d[=u]s"), v. t. [imp. & p. p. Reduced
   (-d[=u]st"),; p. pr. & vb. n. Reducing (-d[=u]"s[i^]ng).]
   [L. reducere, reductum; pref. red-. re-, re- + ducere to
   lead. See Duke, and cf. Redoubt, n.]
   1. To bring or lead back to any former place or condition.
      [Obs.]
      [1913 Webster]

            And to his brother's house reduced his wife.
                                                  --Chapman.
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            The sheep must of necessity be scattered, unless the
            great Shephered of souls oppose, or some of his
            delegates reduce and direct us.       --Evelyn.
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   2. To bring to any inferior state, with respect to rank,
      size, quantity, quality, value, etc.; to diminish; to
      lower; to degrade; to impair; as, to reduce a sergeant to
      the ranks; to reduce a drawing; to reduce expenses; to
      reduce the intensity of heat. "An ancient but reduced
      family." --Sir W. Scott.
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            Nothing so excellent but a man may fasten upon
            something belonging to it, to reduce it.
                                                  --Tillotson.
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            Having reduced
            Their foe to misery beneath their fears. --Milton.
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            Hester Prynne was shocked at the condition to which
            she found the clergyman reduced.      --Hawthorne.
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   3. To bring to terms; to humble; to conquer; to subdue; to
      capture; as, to reduce a province or a fort.
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   4. To bring to a certain state or condition by grinding,
      pounding, kneading, rubbing, etc.; as, to reduce a
      substance to powder, or to a pasty mass; to reduce fruit,
      wood, or paper rags, to pulp.
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            It were but right
            And equal to reduce me to my dust.    --Milton.
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   5. To bring into a certain order, arrangement,
      classification, etc.; to bring under rules or within
      certain limits of descriptions and terms adapted to use in
      computation; as, to reduce animals or vegetables to a
      class or classes; to reduce a series of observations in
      astronomy; to reduce language to rules.
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   6. (Arith.)
      (a) To change, as numbers, from one denomination into
          another without altering their value, or from one
          denomination into others of the same value; as, to
          reduce pounds, shillings, and pence to pence, or to
          reduce pence to pounds; to reduce days and hours to
          minutes, or minutes to days and hours.
      (b) To change the form of a quantity or expression without
          altering its value; as, to reduce fractions to their
          lowest terms, to a common denominator, etc.
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   7. (Chem.) To add an electron to an atom or ion.
      Specifically: To remove oxygen from; to deoxidize.
      (Metallurgy) To bring to the metallic state by separating
      from combined oxygen and impurities; as, metals are
      reduced from their ores. (Chem.) To combine with, or to
      subject to the action of, hydrogen or any other reducing
      agent; as, ferric iron is reduced to ferrous iron;
      aldehydes can be reduced to alcohols by lithium hydride;
      -- opposed to oxidize.
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   8. (Med.) To restore to its proper place or condition, as a
      displaced organ or part; as, to reduce a dislocation, a
      fracture, or a hernia.
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   Reduced iron (Chem.), metallic iron obtained through
      deoxidation of an oxide of iron by exposure to a current
      of hydrogen or other reducing agent. When hydrogen is used
      the product is called also iron by hydrogen.

   To reduce an equation (Alg.), to bring the unknown quantity
      by itself on one side, and all the known quantities on the
      other side, without destroying the equation.

   To reduce an expression (Alg.), to obtain an equivalent
      expression of simpler form.

   To reduce a square (Mil.), to reform the line or column
      from the square.
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   Syn: To diminish; lessen; decrease; abate; shorten; curtail;
        impair; lower; subject; subdue; subjugate; conquer.
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The Collaborative International Dictionary of English v.0.48:

Reducing \Re*du"cing\ (r?*d?"s?ng),
   a & n. from Reduce.
   [1913 Webster]

   Reducing furnace (Metal.), a furnace for reducing ores.

   Reducing pipe fitting, a pipe fitting, as a coupling, an
      elbow, a tee, etc., for connecting a large pipe with a
      smaller one.

   Reducing valve, a device for automatically maintaining a
      diminished pressure of steam, air, gas, etc., in a pipe,
      or other receiver, which is fed from a boiler or pipe in
      which the pressure is higher than is desired in the
      receiver.
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WordNet (r) 3.0 (2006):

reducing
    n 1: any process in which electrons are added to an atom or ion
         (as by removing oxygen or adding hydrogen); always occurs
         accompanied by oxidation of the reducing agent [syn:
         reduction, reducing]
    2: loss of excess weight (as by dieting); becoming slimmer; "a
       doctor supervised her reducing"

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "reducing":
   abating, allaying, alleviating, assuaging, blunting,
   calorie-counting, chastening, cushioning, dampening, damping,
   deadening, diminishing, dulling, easing, lessening, mitigating,
   relaxing, slenderizing, slimming, softening, subduing, tempering,
   weight-watching