Arbitrate (7)
I believe the answer is:
mediate
'arbitrate' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for mediate that I've seen before include "Help settle a dispute" , "try to resolve dispute" , "Act as negotiator between opposing side" , "ie Tamed (anag.)" , "Intervene, act as go-between" .)