Source : Webster's Revised Unabridged Dictionary (1913)

Disappointment \Dis`ap*point"ment\, n. [Cf. F.
   d['e]sappointement.]
   1. The act of disappointing, or the state of being
      disappointed; defeat or failure of expectation or hope;
      miscarriage of design or plan; frustration.

            If we hope for things of which we have not
            thoroughly considered the value, our disappointment
            will be greater our pleasure in the fruition of
            them.                                 --Addison.

            In disappointment thou canst bless.   --Keble.

   2. That which disappoints.

   Syn: Miscarriage; frustration; balk.

Source : WordNet®

disappointment
     n 1: a feeling of dissatisfaction that results when your
          expectations are not realized; "his hopes were so high
          he was doomed to disappointment" [syn: {letdown}]
     2: an act (or failure to act) that disappoints someone [syn: {dashing
        hopes}]