Advantage of backing, say, given to editor (4)
I believe the answer is:
edge
'advantage' is the definition.
(I've seen this before)
'backing say given to editor' is the wordplay.
'backing' says the letters should be written backwards.
'say' becomes 'eg'.
'given to' says to put letters next to each other.
'editor' becomes 'ed'.
'eg' reversed gives 'ge'.
'ge' put after 'ed' is 'EDGE'.
'of' acts as a link.
(Other definitions for edge that I've seen before include "The part farthest from the middle" , "Excitement; boundary" , "Side, brink" , "Steal" , "Line where soething begins or ends" .)