copilot vs courier

copilot

noun
  • A backup or assistant pilot of an aircraft. 

verb
  • To serve as relief or assistant pilot. 

courier

noun
  • A person who looks after and guides tourists. 

  • A company that transports goods. 

  • A user who earns access to a topsite by uploading warez. 

  • A company that delivers messages. 

  • A person who delivers messages. 

verb
  • To deliver by courier. 

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