Adjectives

(s)doubtful, dubiousfraught 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”
(s)doubtful, dubious, dubitable, in questionopen 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)
(s)dubiousnot convinced“they admitted the force of my argument but remained dubious”