Lip; advantage (4)
I believe the answer is:
edge
This clue is a double definition.
'lip' is the first definition.
(I've seen this in another clue)
'advantage' is the second definition.
(having the edge is having an advantage)
(Other definitions for edge that I've seen before include "Move slowly" , "Rim, lip" , "Guitarist with U2" , "Intense/striking quality" , "Sidle, lip" .)