Admitting of doubt; not obvious, clear, or certain; questionable; not decided; not easy to be defined, classed, or named; as, a doubtful case, hue, claim, title, species, and the like.
open to doubt or suspicion; "the candidate's doubtful past"; "he has a dubious record indeed"; "what one found uncertain the other found dubious or downright false"; "it was more than dubitable whether the friend was as influential as she thought"- Karen Horney
fraught with uncertainty or doubt; "they were doubtful that the cord would hold"; "it was doubtful whether she would be admitted"; "dubious about agreeing to go"
Not settled in opinion; undetermined; wavering; hesitating in belief; also used, metaphorically, of the body when its action is affected by such a state of mind; as, we are doubtful of a fact, or of the propriety of a measure.