authentic vs ex cathedra

authentic

adj
  • Conforming to reality and therefore worthy of trust, reliance, or belief. 

  • Of the same origin as claimed; genuine. 

  • Having the final as the lowest note of the mode. 

ex cathedra

prep
  • With authority based on one's rank or office. 

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