Source : Webster's Revised Unabridged Dictionary (1913)

Unhorse \Un*horse"\, v. t. [1 st pref. un- + horse.]
   To throw from a horse; to cause to dismount; also, to take a
   horse or horses from; as, to unhorse a rider; to unhorse a
   carriage. --Cowper.

Source : WordNet®

unhorse
     v : get off (a horse) [syn: {dismount}, {light}, {get off}, {get
         down}]