crown princess vs monarch

crown princess

noun
  • The heiress apparent to the throne in a royal or imperial monarchy. 

  • The wife of a crown prince. 

monarch

noun
  • The ruler of an absolute monarchy or the head of state of a constitutional monarchy. 

  • The monarch butterfly, Danaus plexippus, and others of genus Danaus, found primarily in North America, so called because of the designs on its wings. 

  • A stag which has sixteen or more points or tines on its antlers. 

  • The chief or best thing of its kind. 

  • A police officer. 

  • Any bird of the family Monarchidae. 

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