Source : Webster's Revised Unabridged Dictionary (1913)

Frustrate \Frus"trate\, v. t. [imp. & p. p. {Frustrated}; p. pr.
   & vb. n. {Frustrating}.]
   1. To bring to nothing; to prevent from attaining a purpose;
      to disappoint; to defeat; to baffle; as, to frustrate a
      plan, design, or attempt; to frustrate the will or
      purpose.

            Shall the adversary thus obtain His end and
            frustrate thine ?                     --Milton.

   2. To make null; to nullifly; to render invalid or of no
      effect; as, to frustrate a conveyance or deed.

   Syn: To balk; thwart; foil; baffle; defeat.

Source : WordNet®

frustrating
     adj 1: discouraging by hindering
     2: preventing realization or attainment of a desire [syn: {frustrative},
         {thwarting}]