airmail vs convey

airmail

verb
  • To send mail by air. 

  • To (unintentionally) throw the ball well over a fielder's head where that fielder is unable to make a play on the ball. 

noun
  • The items of mail so carried. 

  • The system of conveying mail using aircraft. 

convey

verb
  • To move (something) from one place to another. 

  • To communicate; to make known; to portray. 

  • To transfer legal rights (to). 

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