The Collaborative International Dictionary of English v.0.48:

Alteration \Al`ter*a"tion\, n. [Cf. F. alt['e]ration.]
   1. The act of altering or making different.
      [1913 Webster]

            Alteration, though it be from worse to better, hath
            in it incoveniences.                  --Hooker.
      [1913 Webster]

   2. The state of being altered; a change made in the form or
      nature of a thing; changed condition.
      [1913 Webster]

            Ere long might perceive
            Strange alteration in me.             --Milton.
      [1913 Webster]

            Appius Claudius admitted to the senate the sons of
            those who had been slaves; by which, and succeeding
            alterations, that council degenerated into a most
            corrupt.                              --Swift.
      [1913 Webster]

WordNet (r) 3.0 (2006):

alteration
    n 1: an event that occurs when something passes from one state
         or phase to another; "the change was intended to increase
         sales"; "this storm is certainly a change for the worse";
         "the neighborhood had undergone few modifications since his
         last visit years ago" [syn: change, alteration,
         modification]
    2: the act of making something different (as e.g. the size of a
       garment) [syn: alteration, modification, adjustment]
    3: the act of revising or altering (involving reconsideration
       and modification); "it would require a drastic revision of
       his opinion" [syn: revision, alteration]