disbelieving vs dubious

disbelieving

adj
  • refusing to believe; skeptical or incredulous 

dubious

adj
  • In disbelief; wavering, uncertain, or hesitating in opinion; inclined to doubt; undecided. 

  • Arousing doubt; questionable; open to suspicion. 

  • Generally considered imprecise or wrong, but not totally unplayable. 

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