Intermediary
Part of speech: adjective
Definition: Intermediate.
Part of speech: noun
Definition: an agent acting as a mediator between sides that may disagree one or several stages of an event which occurs after the start and before the end.
Example sentence: Words are intermediary between thought and things. We express ourselves really not through words, which are only signs, but through what they signify - through things.
Intercessor
Part of speech: noun
Definition: A person who intercedes; a mediator