nightmare vs sigh

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. 

sigh

noun
  • a manifestation of grief; a lament. 

  • A person who is bored. 

  • A deep, prolonged audible inhale and exhale of breath; as when fatigued, frustrated, grieved, or relieved; the act of sighing. 

intj
  • An expression of fatigue, exhaustion, grief, sorrow, frustration, or the like, often used in casual written contexts. 

verb
  • To inhale a larger quantity of air than usual, and immediately expel it; to make a deep single audible respiration, especially as the result or involuntary expression of fatigue, exhaustion, grief, sorrow, frustration, or the like. 

  • To utter sighs over; to lament or mourn over. 

  • To exhale (the breath) in sighs. 

  • To express by sighs; to utter in or with sighs. 

  • To lament; to grieve. 

  • To make a sound like sighing. 

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