Source : Webster's Revised Unabridged Dictionary (1913)

Crestfallen \Crest"fall`en\ (-f?l`'n), a.
   1. With hanging head; hence, dispirited; dejected; cowed.

            Let it make thee crestfullen; Ay, and allay this thy
            abortive pride.                       --Shak.

   2. Having the crest, or upper part of the neck, hanging to
      one side; -- said of a horse.

Source : WordNet®

crestfallen
     adj : brought low in spirit; "left us fatigued and deflated
           spiritually" [syn: {chapfallen}, {chopfallen}, {deflated}]