death penalty vs parricide

death penalty

noun
  • A punishment in which the offender is put to death by the state. 

parricide

noun
  • The killing of a relative, especially a parent. 

  • Someone who kills a relative, especially a parent. 

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

  • Someone who commits treason. 

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