parricide vs regicide

parricide

noun
  • The killing of a ruler, or other authority figure; treason. 

  • The killing of a relative, especially a parent. 

  • Someone who kills a relative, especially a parent. 

  • Someone who commits treason. 

regicide

noun
  • The killing of a king. 

  • One who kills a king. 

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