The Collaborative International Dictionary of English v.0.48:

Dishearten \Dis*heart"en\ (d[i^]s*h[aum]rt"'n), v. t. [imp. & p.
   p. Disheartened (d[i^]s*h[aum]rt"'nd); p. pr. & vb. n.
   Disheartening.] [Pref. dis- + hearten.]
   To discourage; to deprive of courage and hope; to depress the
   spirits of; to deject.
   [1913 Webster]

         Regiments . . . utterly disorganized and disheartened.
                                                  --Macaulay.

   Syn: To dispirit; discourage; depress; deject; deter;
        terrify.
        [1913 Webster]

WordNet (r) 3.0 (2006):

dishearten
    v 1: take away the enthusiasm of [syn: dishearten, put off]
         [ant: cheer, embolden, hearten, recreate]