unhitch

verb

1. To disconnect; to detach; to undo that which is hitched.

   “There is no knowing what further mischief she might have done, had not York promptly sat himself down flat on her head, to prevent her struggling, at the same time calling out, "Unbuckle the black horse! run for the winch and unscrew the carriage pole; cut the trace here—somebody, if you can't unhitch it."”

   “Yet had the whole train and all its bombs gone, had the engine crew merely jumped from the train and run as simple self-preservation would have suggested, or unhitched just the engine to make their escape faster, the whole town would have gone and most of the people with it, leaving just a smoking wasteland. Hundreds would have died.”