fear vs knock on wood

fear

verb
  • To be afraid of (something or someone); to consider or expect (something or someone) with alarm. 

  • To regret. 

  • To worry about, to feel concern for, to be afraid for. 

  • To venerate; to feel awe towards. 

  • To feel fear. 

noun
  • Terrified veneration or reverence, particularly towards God, gods, or sovereigns. 

  • A strong, uncontrollable, unpleasant emotion or feeling caused by actual or perceived danger or threat. 

  • A phobia, a sense of fear induced by something or someone. 

adj
  • Able; capable; stout; strong; sound. 

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. 

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