Oxen coupler (4)
I believe the answer is:
yoke
'oxen coupler' 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 "Oxen harness" , "Wooden crosspiece or burdensome restraint" , "Span (oxen)" , "Burdensome restraint or oppression" , "Eg, pair of draught oxen" .)