go-between vs middleperson

go-between

noun
  • An intermediary or middleman. 

  • A shogi piece, used in chu shogi and larger shogi variants, that can move one step straight forward or straight backwards. 

middleperson

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

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