Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

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

   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.

Source : WordNet®

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}, {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: {bringing close together}]