Source : Webster's Revised Unabridged Dictionary (1913)

Unharness \Un*har"ness\, v. t. [1 st pref. un- + harness.]
   1. To strip of harness; to loose from harness or gear; as, to
      unharness horses or oxen. --Cowper.

   2. To disarm; to divest of armor. --Holinshed.

Source : WordNet®

unharness
     v : remove the harness from; "unharness a horse" [ant: {harness}]