doubtful
adj. B1 Intermediate US //ˈdaʊtfəɫ// UK //dˈaʊtfəl// doubt·ful
adj. not sure if something is true or will happen. You use this when you have doubts and need more proof.
adj. expressing uncertainty about the truth, validity, or likelihood of something.
I am doubtful about his promise.
She remained doubtful of the plan until she saw the detailed budget.
The committee expressed deep doubts regarding the feasibility of the proposal, citing insufficient data and potential risks.
From Middle English doutfull, douteful, equivalent to doubt + -ful.