Promise place with advantage (6)
I believe the answer is:
pledge
'promise' is the definition.
(pledging is a kind of promising)
'place with advantage' is the wordplay.
'place' becomes 'pl' (I've seen this in other clues).
'with' means one lot of letters go next to another.
'advantage' becomes 'edge' (edge is a kind of advantage).
'pl'+'edge'='PLEDGE'
(Other definitions for pledge that I've seen before include "Promise - security" , "Promise (to abstain?)" , "Promise or pawn" , "Covenant" , "Vow; security" .)