Synonyms of doubtful

Adjective

1. doubtful, dubious, dubitable, in question(predicate), questionable (vs. unquestionable)

usage: 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

2. doubtful, dubious, uncertain (vs. certain), unsure (vs. sure), incertain

usage: 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"

3. doubtful, tentative, unsettled (vs. settled)

usage: unsettled in mind or opinion; "drew a few tentative conclusions"

Definition and meaning of doubtful (Dictionary)