of uncertain outcome or result.
admitting of or causing doubt
; uncertain; ambiguous.
unsettled in opinion or belief; undecided; hesitating.
of equivocal or questionable character: His tactics are highly doubtful.
Origin: 1350–1400; Middle English douteful. Related forms
1. undetermined, unsettled, indecisive, dubious, problematic. 2. unsure, indeterminate. 3. irresolute, vacillating, hesitant. Doubtful, dubious, incredulous, skeptical imply reluctance or unwillingness to be convinced. To be doubtful about something is to feel that it is open to question or that more evidence is needed to prove it: to be doubtful about the statements of witnesses. Dubious implies vacillation, unsureness, or suspicion: dubious about suggested methods of manufacture. Incredulous means unwilling or reluctant to believe: incredulous at the good news. Skeptical implies a general disposition to doubt or question: skeptical of human progress. 4. shady.
1, 2. certain.