despair vs knock on wood

despair

verb
  • To be hopeless; to have no hope; to give up all hope or expectation. 

  • To cause to despair. 

noun
  • That which causes despair. 

  • Loss of hope; utter hopelessness; complete despondency. 

  • That which is despaired of. 

knock on wood

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

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

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