Border of hedges (4)
I believe the answer is:
edge
'border' is the definition.
(synonyms)
'of hedges' is the wordplay.
'of' indicates a hidden word.
'EDGE' is hidden in the letters of 'hedges'.
(Other definitions for edge that I've seen before include "Margin, outside limit" , "Rim or slight advantage" , "Rim or sharp side of knife" , "Side, brink" , "Guitarist with U2" .)