parricide vs sororicide

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. 

sororicide

noun
  • A person who kills his or her sister. 

  • The killing of one's sister. 

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