lunchbox vs mailboat

lunchbox

noun
  • A container for transporting meals, especially lunch. 

  • A luggable; an early laptop computer, usually a unit with a handle and a fold-out keyboard. 

  • A simple portable transmitter sometimes used in phreaking. 

  • A lunch packaged in a disposable box to be taken away to eat. 

  • The male genitals when enclosed in clothing. 

  • A cocktail made with beer, orange juice, and almond liqueur. 

mailboat

noun
  • A boat used to transport mail. 

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