imperturbation vs terror

imperturbation

noun
  • Freedom from agitation of mind; calmness. 

terror

noun
  • The action or quality of causing dread; terribleness, especially such qualities in narrative fiction. 

  • Intense dread, fright, or fear. 

  • A night terror. 

  • Terrorism. 

  • Something or someone that causes such fear. 

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