The Collaborative International Dictionary of English v.0.48:

Approximation \Ap*prox`i*ma"tion\ n. [Cf. F. approximation, LL.
   approximatio.]
   1. The act of approximating; a drawing, advancing or being
      near; approach; also, the result of approximating.
      [1913 Webster]

            The largest capacity and the most noble dispositions
            are but an approximation to the proper standard and
            true symmetry of human nature.        --I. Taylor.
      [1913 Webster]

   2. An approach to a correct estimate, calculation, or
      conception, or to a given quantity, quality, etc.
      [1913 Webster]

   3. (Math.)
      (a) A continual approach or coming nearer to a result; as,
          to solve an equation by approximation.
      (b) A value that is nearly but not exactly correct.
          [1913 Webster]

WordNet (r) 3.0 (2006):

approximation
    n 1: an approximate calculation of quantity or degree or worth;
         "an estimate of what it would cost"; "a rough idea how long
         it would take" [syn: estimate, estimation,
         approximation, idea]
    2: the quality of coming near to identity (especially close in
       quantity)
    3: an imprecise or incomplete account; "newspapers gave only an
       approximation of the actual events"
    4: the act of bringing near or bringing together especially the
       cut edges of tissue [syn: approximation, bringing close
       together]