1
[ADJ-GRADED 能被表示程度的副词或介词词组修饰的形容词]未必的；不大可能的 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...
有一段时间他似乎根本不会搬家。
It is doubtful whether Tweed, even with his fluent French, passed for one of the locals...
尽管特威德能说一口流利的法语，他是否能被当作当地人还很难说。
Whether the authorities will allow inspection is highly doubtful.
当局是否允许检查还是个大问号。
2
[ADJ-GRADED 能被表示程度的副词或介词词组修饰的形容词]怀疑的；疑惑的；拿不定主意的 If you are
doubtful about something, you feel unsure or uncertain about it.
3
[ADJ-GRADED 能被表示程度的副词或介词词组修饰的形容词](质量或价值)低劣的，不可靠 If you say that something is
of doubtful quality or value, you mean that it is of low quality or value.
[usu ADJ n]
[disapproval]
...selling something that is overpriced or of doubtful quality...
售卖漫天要价或质量低劣的东西
They also seemed of very doubtful value.
它们好像也没有多大价值。
...information that he described as having doubtful reliability.
据他所称未必可靠的消息
4
[ADJ-GRADED 能被表示程度的副词或介词词组修饰的形容词](通常指运动员因伤)不大可能参加（比赛）的 If a sports player is
doubtful for a match or event, he or she seems unlikely to play, usually because of injury.
[oft ADJ for n]
[JOURNALISM 新闻]
Usage Note :
Do not confuse doubtful, dubious, and suspicious. If you feel doubtful about something, you are unsure about it or about whether it will happen or be successful. Do you feel insecure and doubtful about your ability?... It was doubtful he would ever see her again. If you are dubious about something, you are not sure whether it is the right thing to do. Alison sounded very dubious... The men in charge were a bit dubious about taking women on. If you describe something as dubious, you think it is not completely honest, safe, or reliable. ...his dubious abilities as a teacher. If you are suspicious of a person, you do not trust them and think they might be involved in something dishonest or illegal. I am suspicious of his intentions... Miss Lenaut had grown suspicious. If you describe something as suspicious, it suggests behaviour that is dishonest, illegal, or dangerous. He listened for any suspicious sounds. ...in suspicious circumstances.
不要混淆 doubtful, dubious, suspicious。doubtful 指不确定某事或不确定其是否会发生或成功：Do you feel insecure and doubtful about your ability（你对自己的能力缺乏信心，抱有怀疑吗），It was doubtful he would ever see her again（他会不会再见到她还说不准）。dubious 指拿不准做某事是否正确：Alison sounded very dubious（艾利森听上去犹豫不决），The men in charge were a bit dubious about taking women on（几位男性负责人有点儿拿不准要不要招女员工）。dubious 还可指某事物不完全可信、安全或可靠：his dubious abilities as a teacher（他的教学能力令人怀疑）。suspicious 指不信任某人，怀疑其从事欺骗性或不法活动：I am suspicious of his intentions（我怀疑他动机不纯），Miss Lenaut had grown suspicious（莱诺小姐已经起了疑心）。suspicious 还可指某人的行为可疑、不诚实、涉及非法或具有危险性：He listened for any suspicious sounds（他注意倾听任何可疑的声音），in suspicious circumstances（在可疑的情势下）。