peril vs threaten

peril

verb
  • To cause to be in danger; to imperil; to risk. 

noun
  • A situation of serious and immediate danger. 

  • An event which causes a loss, or the risk of a specific such event. 

  • Something that causes, contains, or presents danger. 

threaten

verb
  • To menace, or be dangerous. 

  • To portend, or give a warning of. 

  • To call into question the validity of (a belief, idea, or viewpoint); to challenge. 

  • He threatened me with a knife. 

  • To make a threat against someone; to use threats. 

  • To be close to equaling or surpassing (a record, etc.) 

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