Wellington boot vs gumboot

Wellington boot

noun
  • One of a pair of Wellington boots. 

gumboot

noun
  • A chiton (kind of marine mollusc). 

  • Generic black tea. 

  • A type of boot made of rubber. 

  • A style of popular music traditionally associated with gold miners. 

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