0 If something is doubtful, it probably will not happen -- dubbio, incerto
It’s doubtful whether he’s going to come. È incerto se verrà.
1 not feeling certain about something -- dubbioso, incerto
The teacher is doubtful about having parents working as classroom assistants. L’insegnante è incerto sul far fare ai genitori gli assistenti in classe.
2 feeling doubt; uncertain what to think, expect etc -- dubbioso, incerto
3 able to be doubted; not clear -- incerto
4 uncertain but rather unlikely, unhopeful etc -- incerto
a doubtful improvement.
It is doubtful whether this will work
5 suspicious -- ambiguo, equivoco