authentic vs unbelievable

authentic

adj
  • Of the same origin as claimed; genuine. 

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

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

unbelievable

adj
  • Not to be believed. 

  • Amazing, incredible; so surprising it is almost unable to believe. 

  • Implausible or improbable. 

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