From Longman Dictionary of Contemporary Englishmediatorme‧di‧a‧tor /ˈmiːdieɪtə $ -ər/ noun [countable] a person or organization that tries to end a quarrel between two people, groups, countries etc by discussion → intermediary
Examples from the Corpus
mediator• I see no basis for meaningful comparison between solicitors and mediators.• There were no official mediators, licensed by an ecclesiastical hierarchy or set apart by apostolic ordination.• There is also an independent service with trained mediators, most of them solicitors. 