PI vs peeper

PI

peeper

noun
  • The eye. 

  • An animal, such as some frogs, having a shrill, high-pitched call. 

  • Someone who peeps; a spy. 

  • A chicken just breaking the shell; a young bird. 

  • A peeping tom. 

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