uncouple

verb

1. (transitive)To disconnect or detach one thing from another.

   “We uncoupled the trailer and left it behind.”

   “The railway workers uncoupled the cars near the tail end of the train.”

   “On arrival at Spiez, the locomotive (No. 206) was immediately uncoupled and drew ahead to enable an Italian through coach from Interlaken to Milan to be loose shunted (with passengers aboard and controlled by means of its handbrake) on to the front of the train.”

   “The shunter has a lightweight portable radio transmitter by which, as he uncouples an incoming train into cuts for marshalling, he informs the Traffic Office of the number of wagons in each cut and its siding; [...].”

   “The driver remained at his post, while telling fireman Jim Nightall to get down on the track and run back to uncouple the burning wagon from the rest.”

2. (transitive)To come loose.
3. (transitive)To loose, as dogs, from their couples.