cicerone vs mentor

cicerone

noun
  • A guide who accompanies visitors and sightseers to museums, galleries, etc., and explains matters of archaeological, antiquarian, historic or artistic interest.. 

mentor

noun
  • A wise and trusted counselor or teacher. 

verb
  • To act as someone's mentor. 

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