airmail vs voicemail

airmail

noun
  • The system of conveying mail using aircraft. 

  • The items of mail so carried. 

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. 

voicemail

noun
  • An individual message on such a system. 

  • A computerized interactive system for storing, processing and reproducing verbal messages left through a conventional telephone network. 

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