The Collaborative International Dictionary of English v.0.48:

Chopfallen \Chop`fall`en\, a.
   Having the lower chop or jaw depressed; hence, crestfallen;
   dejected; dispirited; downcast. See Chapfallen.
   [1913 Webster]

WordNet (r) 3.0 (2006):

chopfallen
    adj 1: brought low in spirit; "left us fatigued and deflated
           spiritually" [syn: chapfallen, chopfallen,
           crestfallen, deflated]