pannikin vs water boiler

pannikin

noun
  • A durable cup or other vessel used for drinking made of metal and coated in enamel. 

  • The contents of such a vessel. 

water boiler

noun
  • An electric device which heats water up to boiling temperature. 

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