1 [usu pred 通常作表语] ~ (about sth/doing sth) (of a person) feeling doubt; unsure （指人）感到怀疑, 不能确定
*feel doubtful about (the wisdom of) going/about whether to go or not 拿不定主意去不去（不知道应否去）.
2 causing doubt; uncertain 令人生疑的; 不肯定的
*The weather looks rather doubtful, ie unsettled. 天气看来靠不住（可能会变天）.
* a doubtful (ie unreliable) ally 不可靠的盟友
* It's a doubtful blessing, ie It may or may not be one. 这是不是福不好说.
3 unlikely; improbable 未必的; 不大可能的
*It is extremely doubtful that anyone survived the explosion. 在那场爆炸中很难有幸存者.
4 [attrib 作定 语] possibly dishonest, disreputable, etc; causing suspicion; questionable （诚实、名声等）不大好的, 可疑的, 有问题的
*a rather doubtful character, neighbourhood,past 很可疑的人物、邻居、过去.
probably not true or not likely to happen Prospects for a lasting peace remain doubtful.it is doubtful if/whether It was doubtful whether the patient would survive the operation.it is doubtful that It is doubtful that the missing airmen will ever be found.
not sure that something is true or right 'Everything's going to be all right, you'll see.' Jenny looked doubtful .doubtful if/whether I'm still doubtful whether I should accept this job.doubtful about (doing) sth At first we were doubtful about employing Charlie.
unlikely to be successful Already the whole scheme was looking increasingly doubtful.
probably not good
= dubious Here the tap water is of doubtful quality.>doubtfullyadv
1. Bonpland was doubtful whether, even then, it was safe. 即使如此，庞普朗还是怀疑这水是否安全。
2. But if he'd been able to speak with an educated accent in those early short comedy movies, it's doubtful if he would have achieved world fame. 但假如他在早期那些短小喜剧电影中能操一口受过教育的人的口音，那么他是否会闻名世界就值得怀疑了，
3. Though we may enjoy reading about the lives of others, it is extremely doubtful whether we would equally enjoy reading about ourselves. 我们都喜欢看关于别人生活的报道，但是否同样喜欢看关于自己生活的报道，就很难说了。
4. He is a doubtful character. 他是个可疑的人物。
5. One woman admits she was doubtful until she tried Imedeen herself. 一位女士承认自己在试用"伊美婷"之前是有怀疑的。
6. I am doubtful about the propriety of granting such a request. 我怀疑答应这项要求是否合适.