Fencing piece (4)
I believe the answer is:
rail
'fencing piece' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for rail that I've seen before include "method of transport" , "Water bird; bar" , "Complain bitterly - wading bird" , "Bar of track or fence" , "Scold, berate" .)