dubious vs unchallenged

dubious

adj
  • Arousing doubt; questionable; open to suspicion. 

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

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

unchallenged

adj
  • Lacking experience due to lack of challenges; untested. 

  • Not having any challengers. 

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