1) To release oxen from harness 2) Unharness 3) Unyoke 
• (v. t. & i.) To unyoke or disengage, as oxen from a wagon.
Out·span' transitive verb & i. [ Dutch uitspannen .] To unyoke or disengage, as oxen from a wagon. [ S. Africa]
[v] - remove the yoke or harness from, as of a draft animal