matricide vs parricide

matricide

noun
  • A person who kills his or her mother. 

  • The killing of one's mother. 

parricide

noun
  • Someone who kills a relative, especially a parent. 

  • The killing of a relative, especially a parent. 

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

  • Someone who commits treason. 

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