Coupling device (4)
I believe the answer is:
yoke
'coupling device' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for yoke that I've seen before include "wooden frame" , "Wooden crosspiece or burdensome restraint" , "Frame joining draught oxen at the necks" , "Old harness or oppression" , "Oxen harness" .)