1.
If it is doubtful that something will happen, it seems unlikely to happen or you are uncertain whether it will happen.
For a time it seemed doubtful that he would move at all...
It is doubtful whether Tweed, even with his fluent French, passed for one of the locals...
ADJ: usu v-link ADJ, oft it v-link ADJ that/wh
2.
If you are doubtful about something, you feel unsure or uncertain about it.
I was still very doubtful about the chances for success...
Why did he sound so doubtful?
= dubious
ADJ: usu v-link ADJ, oft ADJ about n
• doubtfully
Keeton shook his head doubtfully.
= dubiously
ADV: ADV after v
3.
If you say that something is of doubtful quality or value, you mean that it is of low quality or value.
...selling something that is overpriced or of doubtful quality...
= dubious
ADJ: usu ADJ n [disapproval]
4.
If a sports player is doubtful for a match or event, he or she seems unlikely to play, usually because of injury. (JOURNALISM)
ADJ: oft ADJ for n