The Collaborative International Dictionary of English v.0.48:

Conversion \Con*ver"sion\, n. [L. conversio: cf. F. conversion.
   See Convert.]
   1. The act of turning or changing from one state or condition
      to another, or the state of being changed; transmutation;
      change.
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            Artificial conversion of water into ice. --Bacon.
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            The conversion of the aliment into fat. --Arbuthnot.
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   2. The act of changing one's views or course, as in passing
      from one side, party, or from of religion to another;
      also, the state of being so changed. "Conversion to
      Christianity." --Prescott.
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   3. (Law) An appropriation of, and dealing with the property
      of another as if it were one's own, without right; as, the
      conversion of a horse.
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            Or bring my action of conversion
            And trover for my goods.              --Hudibras.
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   4. (Logic) The act of interchanging the terms of a
      proposition, as by putting the subject in the place of the
      predicate, or the contrary.
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   5. (Math.) A change or reduction of the form or value of a
      proposition; as, the conversion of equations; the
      conversion of proportions.
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   6. (Mil.)
      (a) A change of front, as a body of troops attacked in the
          flank.
      (b) A change of character or use, as of smoothbore guns
          into rifles.
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   7. (Theol.) A spiritual and moral change attending a change
      of belief with conviction; a change of heart; a change
      from the service of the world to the service of God; a
      change of the ruling disposition of the soul, involving a
      transformation of the outward life.
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            He oft
            Frequented their assemblies, . . . and to them
            preached
            Conversion and repentance, as to souls
            In prison under judgments imminent.   --Milton.
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WordNet (r) 3.0 (2006):

conversion
    n 1: an event that results in a transformation [syn:
         conversion, transition, changeover]
    2: a change in the units or form of an expression: "conversion
       from Fahrenheit to Centigrade"
    3: a successful free throw or try for point after a touchdown
    4: a spiritual enlightenment causing a person to lead a new life
       [syn: conversion, rebirth, spiritual rebirth]
    5: (psychiatry) a defense mechanism represses emotional
       conflicts which are then converted into physical symptoms
       that have no organic basis
    6: a change of religion; "his conversion to the Catholic faith"
    7: interchange of subject and predicate of a proposition
    8: act of exchanging one type of money or security for another
    9: the act of changing from one use or function or purpose to
       another