Promise place on Fringe (6)
I believe the answer is:
pledge
'promise' is the definition.
(pledging is a kind of promising)
'place on fringe' is the wordplay.
'place' becomes 'pl' (I've seen this in other clues).
'on' is a charade indicator (letters next to each other).
'fringe' becomes 'edge' ('edge' can be a synonym of 'fringe').
'pl'+'edge'='PLEDGE'
(Other definitions for pledge that I've seen before include "Plight" , "Vow, affirm" , "Covenant" , "Promise - security" , "Vow; security" .)