hauberk vs third class

hauberk

noun
  • A coat of mail; especially, the long coat of mail of the European Middle Ages, as contrasted with the habergeon, which is shorter and sometimes sleeveless. 

  • A similar shirt of scale mail, plate, leather, or other armor material. 

third class

noun
  • A reduced-rate mail service for printed matter. 

  • The cheapest accommodation on a train or ship. 

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