archdiocese vs diocese

archdiocese

noun
  • An area administered by an archbishop; the ecclesiastical hierarchy of this area, also under the archbishop. 

diocese

noun
  • Region administered by a bishop. 

  • Administrative division of the later Roman Empire, starting with the tetrarchy. 

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