knock on wood vs purport

knock on wood

verb
  • To take a customary action to ward off some misfortune that is believed to be attracted by a presumptuous statement. 

intj
  • Hopefully; a self-directive to undertake the customary action to ward off bad luck. 

purport

verb
  • To convey, imply, or profess (often falsely or inaccurately). 

  • To intend. 

noun
  • import, intention or purpose 

How often have the words knock on wood and purport occurred in a corpus of books? (source: Google Ngram Viewer )