foretoken vs prewarn

foretoken

verb
  • To betoken beforehand; prognosticate; foreshadow; give warning of; presage. 

noun
  • A prognostic; a premonitory sign; warning or presentiment. 

prewarn

verb
  • To warn beforehand; to forewarn. 

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