intermediary:
(plural: ‘intermediaries‘; pronunciation: the letter ‘i’ rhymes with the letter ‘i’ in “ink”)

an intermediary trying to sort out a disagreement between two persons
a person going/acting between two other persons or groups of persons in disagreement, usually so as to join them;
a mediator; (a middleman);
an experienced and competent person/agent whose job is to work as a bridge or ‘junction point’ between two or more businesspersons or companies in order to work out a deal smoothly and successfully,

an intermediary from the intermediary law office of Madonna M. Finney, Adoption Attorney, USA, helping a married childless couple adopt a child
Any intermediary must be a person or office that has nothing to do with the parties — persons, businesses, offices — involved in a deal; he/she must be impartial and have in-depth knowledge of the deal or transaction he/she dealing with.
There are several kinds of intermediaries some of which are registered or licensed that help people in different ways.
When the manager and the assistant manager were at loggerheads over a simple procedure, the managers wise secretary acted as an intermediary and helped them to find a compromise.
Intermediaries in political or diplomatic issues are given extra security and special privileges as their lives may be at risk in some delicate negotiations.
