moan vs nightmare

moan

verb
  • To grieve. 

  • To complain; to grumble. 

  • To say in a moan, or with a moaning voice. 

  • To make a moan or similar sound. 

noun
  • a low, mournful cry of pain, sorrow or pleasure 

nightmare

verb
  • To have a 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. 

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