terrible vs unbelievable

terrible

adj
  • Unpleasant; disagreeable. 

  • Intense; extreme in degree or extent. 

  • Dreadful; causing terror, alarm and fear; awesome 

  • Formidable, powerful. 

  • Very bad; lousy. 

adv
  • In a terrible way; to a terrible extent; terribly; awfully. 

unbelievable

adj
  • Implausible or improbable. 

  • Not to be believed. 

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

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