apostate vs stool pigeon

apostate

noun
  • One who, after having received sacred orders, renounces his clerical profession. 

  • A person who has renounced a religion or faith. 

adj
  • Guilty of apostasy. 

stool pigeon

noun
  • An informer to the authorities, especially one who gives up criminal associates. 

  • A pigeon tied to a stool by a piece of twine, used as a decoy to entice free-flying birds to the ground to be shot or trapped. 

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