Definitions of intermediary
someone who helps to arrange discussions between other people; a third party negotiator who carries messages between people who are unwilling or unable to meet; a mediator
Egypt is intimately involved with the Palestinian problem, acting as an intermediary between Israel and Hamas in the Gaza Strip.
someone who helps to arrange business deals between other people
Under the new rules, intermediaries such as lawyers, tax advisors, and accountants that design, promote or implement certain 'arrangements' are required to report them to tax authorities.