1) Disconnect a trailer 2) Free Dobbin from the traces 3) Free the trailer 4) Let go 5) Release from a post 6) Remove a trailer 7) To detach 8) To disconnect 9) To free from attachment 10) To undo that which is hitched 11) Undo 1) Unharness 2) Unyoke 
• (v. t.) To free from being hitched, or as if from being hitched; to unfasten; to loose; as, to unhitch a horse, or a trace.
[v] - unfasten or release from or as if from a hitch
to free from attachment; unfasten: to unhitch a locomotive from a train.