heroism vs nightmare

heroism

noun
  • The qualities characteristic of a hero, such as courage, bravery, fortitude, selflessness, etc.; the display of such qualities. 

nightmare

noun
  • Any bad, miserable, difficult or terrifying situation or experience that arouses anxiety, terror, agony or great displeasure. 

  • A very bad or frightening dream. 

  • A feeling of extreme anxiety or suffocation experienced during sleep; Sleep paralysis. 

verb
  • To have a nightmare. 

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