intermediary vs middleperson

intermediary

noun
  • A person or organisation in an intermediate position (in a transaction, agreement, supply chain etc.) 

  • One or several stages of an event which occurs after the start and before the end. 

  • An agent acting as a mediator between sides to facilitate agreement or cooperation. 

adj
  • Intermediate. 

middleperson

noun
  • An intermediate dealer of any gender; a middleman or middlewoman. 

How often have the words intermediary and middleperson occurred in a corpus of books? (source: Google Ngram Viewer )