The Collaborative International Dictionary of English v.0.48:

Inversion \In*ver"sion\, n. [L. inversio: cf. F. inversion. See
   Invert.]
   [1913 Webster]
   1. The act of inverting, or turning over or backward, or the
      state of being inverted.
      [1913 Webster]

   2. A change by inverted order; a reversed position or
      arrangement of things; transposition.
      [1913 Webster]

            It is just the inversion of an act of Parliament;
            your lordship first signed it, and then it was
            passed among the Lords and Commons.   --Dryden.
      [1913 Webster]

   3. (Mil.) A movement in tactics by which the order of
      companies in line is inverted, the right being on the
      left, the left on the right, and so on.
      [1913 Webster]

   4. (Math.) A change in the order of the terms of a
      proportion, so that the second takes the place of the
      first, and the fourth of the third.
      [1913 Webster]

   5. (Geom.) A peculiar method of transformation, in which a
      figure is replaced by its inverse figure. Propositions
      that are true for the original figure thus furnish new
      propositions that are true in the inverse figure. See
      Inverse figures, under Inverse.
      [1913 Webster]

   6. (Gram.) A change of the usual order of words or phrases;
      as, "of all vices, impurity is one of the most
      detestable," instead of, "impurity is one of the most
      detestable of all vices."
      [1913 Webster]

   7. (Rhet.) A method of reasoning in which the orator shows
      that arguments advanced by his adversary in opposition to
      him are really favorable to his cause.
      [1913 Webster]

   8. (Mus.)
      (a) Said of intervals, when the lower tone is placed an
          octave higher, so that fifths become fourths, thirds
          sixths, etc.
      (b) Said of a chord, when one of its notes, other than its
          root, is made the bass.
      (c) Said of a subject, or phrase, when the intervals of
          which it consists are repeated in the contrary
          direction, rising instead of falling, or vice versa.
      (d) Said of double counterpoint, when an upper and a lower
          part change places.
          [1913 Webster]

   9. (Geol.) The folding back of strata upon themselves, as by
      upheaval, in such a manner that the order of succession
      appears to be reversed.
      [1913 Webster]

   10. (Chem.) The act or process by which cane sugar (sucrose),
       under the action of heat and acids or enzymes (as
       diastase), is broken or split up into grape sugar
       (dextrose), and fruit sugar (levulose); also, less
       properly, the process by which starch is converted into
       grape sugar (dextrose).
       [1913 Webster]

   Note: The terms invert and inversion, in this sense, owe
         their meaning to the fact that the plane of
         polarization of light, which is rotated to the right by
         cane sugar, is turned toward the left by levulose.
         [1913 Webster]

   11. (Meteorology) A reversal of the usual temperature
       gradient of the atmosphere, in which the temperature
       increases with increased altitude, rather than falling.
       Called also temperature inversion.

   Note: This condition in the vicinity of cities can give rise
         to a severe episode of atmospheric pollution, as it
         inhibits normal circulation of the air.
         [PJC]

   12. (Electricity) The conversion of direct current into
       alternating current; the inverse of rectification. See
       inverted rectifier.
       [PJC]

   13. (Genetics) A portion of the genome in which the DNA has
       been turned around, and runs in a direction opposite to
       its normal direction, and consequently the genes are
       present in the reverse of their usual order.
       [PJC]

WordNet (r) 3.0 (2006):

inversion
    n 1: the layer of air near the earth is cooler than an overlying
         layer
    2: abnormal condition in which an organ is turned inward or
       inside out (as when the upper part of the uterus is pulled
       into the cervical canal after childbirth)
    3: a chemical process in which the direction of optical rotation
       of a substance is reversed from dextrorotatory to levorotary
       or vice versa
    4: (genetics) a kind of mutation in which the order of the genes
       in a section of a chromosome is reversed
    5: the reversal of the normal order of words [syn: anastrophe,
       inversion]
    6: (counterpoint) a variation of a melody or part in which
       ascending intervals are replaced by descending intervals and
       vice versa
    7: a term formerly used to mean taking on the gender role of the
       opposite sex [syn: inversion, sexual inversion]
    8: turning upside down; setting on end [syn: inversion,
       upending]
    9: the act of turning inside out [syn: inversion, eversion,
       everting]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "inversion":
   about-face, addition, approximation, differentiation, division,
   equation, evolution, extrapolation, integration, interpolation,
   involution, multiplication, notation, practice, proportion,
   reduction, reversal, reverse, reversion, subtraction,
   transformation, turn, turnabout, turning, volte-face