The Collaborative International Dictionary of English v.0.48:

Reduction \Re*duc"tion\ (r[-e]*d[u^]k"sh[u^]n), n. [F.
   r['e]duction, L. reductio. See Reduce.]
   1. The act of reducing, or state of being reduced; conversion
      to a given state or condition; diminution; conquest; as,
      the reduction of a body to powder; the reduction of things
      to order; the reduction of the expenses of government; the
      reduction of a rebellious province.
      [1913 Webster]

   2. (Arith. & Alg.) The act or process of reducing. See
      Reduce, v. t., 6. and To reduce an equation, To
      reduce an expression, under Reduce, v. t.
      [1913 Webster]

   3. (Astron.)
      (a) The correction of observations for known errors of
          instruments, etc.
      (b) The preparation of the facts and measurements of
          observations in order to deduce a general result.
          [1913 Webster]

   4. The process of making a copy of something, as a figure,
      design, or draught, on a smaller scale, preserving the
      proper proportions. --Fairholt.
      [1913 Webster]

   5. (Logic) The bringing of a syllogism in one of the
      so-called imperfect modes into a mode in the first figure.
      [1913 Webster]

   6. (Chem. & Metal.) The act, process, or result of
      reducing[7]; as, the reduction of iron from its ores; the
      reduction of an aldehyde into an alcohol.
      [1913 Webster]

   7. (Med.) The operation of restoring a dislocated or
      fractured part to its former place.
      [1913 Webster]

   Reduction ascending (Arith.), the operation of changing
      numbers of a lower into others of a higher denomination,
      as cents to dollars.

   Reduction descending (Arith.), the operation of changing
      numbers of a higher into others of a lower denomination,
      as dollars to cents.
      [1913 Webster]

   Syn: Diminution; decrease; abatement; curtailment;
        subjugation; conquest; subjection.
        [1913 Webster]