Side with upper hand (4)
I believe the answer is:
edge
I believe this clue is a triple definition!
'side' is the first definition.
(I know that edge is a type of side)
'with' is a link.
'upper' is the second definition.
(thesaurus)
'hand' is the third definition.
(I have seen 'Upper hand' mean 'edge' so perhaps 'hand' could also mean 'edge')
(Other definitions for edge that I've seen before include "Golden ingot" , "marginal advantage" , "Excitement; boundary" , "Cutting side as of knife, or margin" , "Border, fringe" .)