assassin vs regicide

assassin

noun
  • Someone who intentionally kills a person, especially a professional who kills a public or political figure. 

  • Any ruthless killer. 

  • A member of the Nizari Ismaili Muslim community of the Alamut Period. 

verb
  • To assassinate. 

regicide

noun
  • One who kills a king. 

  • The killing of a king. 

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