dubious vs unproper

dubious

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

  • Arousing doubt; questionable; open to suspicion. 

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

unproper

adj
  • Improper, not according with good standards of behaviour; indecent, indecorous. 

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