In favour of compromise (3)
I believe the answer is:
pro
'in favour' is the definition.
(I've seen this before)
'of compromise' is the wordplay.
'of' says the answer is hidden in the clue.
'PRO' can be found hidden inside 'compromise'.
(Other definitions for pro that I've seen before include "Expert (abbr)" , "Golfer" , "In favour of; advantage" , "Favouring the professional" , "In brief, he's no amateur" .)