crown jewels vs tiara

crown jewels

noun
  • The jewelry that accompany the office of rulership in a monarchy, i.e. crown, scepter, signet ring, etc. 

  • The male genitalia. 

tiara

noun
  • The papal crown. 

  • An ornamental coronet. 

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