adj.(形容词)

1. 怀疑的，可疑的， 令人生疑的，不太相信的
2. 含糊的，疑惑的，有疑问的
3. 难以预测的
4. 不明确的
5. 不好的，未必好的
6. 低劣的
7. 未必货真价实的
8. 靠不住的，拿不准的

adj.(形容词)

1. 难以预测的,未定的 uncertain; not settled
2. 怀疑的,可疑的 not trusting; questionable

Adjective:

1. open to doubt or suspicion;

   "the candidate's doubtful past"
   "he has a dubious record indeed"
   "what one found uncertain the other found dubious or downright false"
   "it was more than dubitable whether the friend was as influential as she thought"
   

2. fraught with uncertainty or doubt;

   "they were doubtful that the cord would hold"
   "it was doubtful whether she would be admitted"
   "dubious about agreeing to go"
   

3. unsettled in mind or opinion;

   "drew a few tentative conclusions"
   

1.未必的;不大可能的
If it isdoubtful that something will happen, it seems unlikely to happen or you are uncertain whether it will happen.

e.g. For a time it seemeddoubtful that he would move at all...
有一段时间他似乎根本不会搬家。
e.g. It isdoubtful 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。

2.怀疑的;疑惑的;拿不定主意的
If you aredoubtful about something, you feel unsure or uncertain about it.

e.g. I was still verydoubtful about the chances for success...
我对能否成功仍然深表怀疑。
e.g. Why did he sound sodoubtful?
为什么他听上去如此不确定？

doubtfully
Keeton shook his head doubtfully.
基顿疑惑地摇了摇头。

3.(质量或价值)低劣的，不可靠
If you say that something isof doubtful quality or value, you mean that it is of low quality or value.

e.g. ...selling something that is overpriced or ofdoubtful quality...
售卖漫天要价或质量低劣的东西
e.g. They also seemed of verydoubtful value.
它们好像也没有多大价值。

4.(通常指运动员因伤)不大可能参加（比赛）的
If a sports player isdoubtful for a match or event, he or she seems unlikely to play, usually because of injury.

e.g. Forsyth isdoubtful for tonight's game with a badly bruised leg.
福赛斯腿部严重擦伤，不大可能参加今晚的比赛。

Do not confusedoubtful,dubious, andsuspicious. If you feeldoubtful 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 aredubious 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 asdubious, you think it is not completely honest, safe, or reliable....his dubious abilities as a teacher. If you aresuspicious 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 assuspicious, 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）。

1. 可疑的：1907年,AMA把当时160所医学院分成可接受(Acceptable)、可疑的(doubtful)、不可接受(Unacceptable)三类. 很多美国医生对AMA日益因循守旧、自私自利的姿态非常不满,他们不但不参加AMA,而且还成立了自己的组织,与AMA针锋相对,反其道而行之.

2. doubtful是什么意思

2. 表示不是很肯定：◆positively adv. 绝对地,完全地 | doubt;doubtful; uncertain; dubious 表示不是很肯定 | ◆disadvantage n. 短处,缺点

3. doubtful什么意思

3. 怀疑的,可疑的：doubt 怀疑,疑问,不相信 |doubtful 怀疑的,可疑的 | doubtless 无疑的,很可能的

用作定语～+ n.

1. This is a doubtful battle.
   这是一场胜负难测的战争。
2. Let's try to clear up our difficult and doubtful points.
   让我们设法把难处和疑点解决一下。

用作表语S+be+～

1. The weather looks very doubtful.
   这天气很靠不住。
2. Everyone was doubtful at first, but his statement in detail held up.
   起初大家都怀疑,但他的详细叙述证明情况属实。

S+be+～+ prep .-phrase

1. I feel very doubtful about this.
   我对这点很怀疑。
2. I feel doubtful about his ability to do the work.
   我怀疑他有无做这件事的能力。
3. He was doubtful of the patient's recovery.
   他怀疑病人是否痊愈。
4. I am very doubtful of that.
   我很疑心那件事。

S+be+～+wh-to- v

1. I'm doubtful where to go.
   该往哪里去我心中无底。

S+be+～+wh-clause

1. I feel doubtful what I ought to do.
   我不知该做什么。
2. She is doubtful whether her mother really likes the present.
   她怀疑她母亲是否真喜欢那个礼物。

It is/was+～+that/wh-/if-clause

1. It is doubtful if our resources will hand out for more than two or three days more.
   我们的资源能否再维持两三天以上,值得怀疑。
2. It is doubtful whether it is true or not.
   这事的真假是可疑的。
3. It is not doubtful that he will give up smoking.
   他会戒烟是不用怀疑的。

• A doubtful Passage in a Latin Poet.

  出自：Addison

• The question whether certain doubtful forms should be ranked as species or varieties.

  出自：C. Darwin

• It was doubtful if he knew who Andrew Jackson was.

  出自：Scott Fitzgerald

• A change which is not an unquestionable improvement is a doubtful blessing.

  出自：E. F. Schumacher

It is doubtful whether it is true or not.

这件事的真假是可疑的。

The fact that he won the first place is doubtful.

他得了第一名是让人可疑的。

He is an author of doubtful reputation.

他是一位名声不太好的作家。

The ethics of his decision are doubtful.

他的这一决定是否合乎道德规范值得怀疑。

I am doubtful about the propriety of granting such a request.

我怀疑答应这项要求是否合适。

It is doubtful whether the old man will recover from the operation.

那老人手术后是否会康复难以确定。

Rose was doubtful about the whole idea.

罗斯对整个设想持怀疑态度。

He was doubtful about accepting extra work.

他拿不定主意是否接受额外工作。

It's doubtful if this painting is a Picasso.

这未必就是毕加索的画。

With her injuries it's doubtful that she'll ever walk again.

她多处受伤，今后能否行走还很难说。

It's doubtful whether the car will last another year.

这辆汽车未必还能用上一年。

He is injured and is doubtful for the game tomorrow (= unlikely to play) .

他受了伤，明天未必能参赛。

At the beginning of the war things were looking very doubtful.

战争刚开始时，形势看上去很不明朗。

This wine is of doubtful quality.

这酒的质量有问题。

Why did he sound so doubtful?

为什么他听上去如此不确定？

...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。

Forsyth is doubtful for tonight's game with a badly bruised leg.

福赛斯腿部严重擦伤，不大可能参加今晚的比赛。

I was still very doubtful about the chances for success...

我对能否成功仍然深表怀疑。

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。

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。

I am very doubtful of that.

我很疑心那件事.

It is doubtful whether he can read my fortune or not.

他能否算出我的运气还是个疑问.

Provisions for doubtful debts increased to eight million pounds.

疑账准备金增加到八百万英镑.

He felt very doubtful of the outcome.

关于结果他感到非常疑惑.

I am doubtful whether it is true.

我怀疑那是否真实.

It is doubtful if dehydrated fruit will make much headway.

脱水水果是否有多大进步尚难予料.

It is doubtful that he will come.

他会不会来值得怀疑.

As soon as he finished, his supporters applauded vigorously, but most of the masses were taken aback and exchanged doubtful glances.

他的话完了, 他的几个支持者拼命地鼓掌, 而更多的人却噤若寒蝉,面面相觑.

Let's try to clear up our difficult and doubtful points.

让我们设法把难处和疑点解决一下.

The day is doubtful.

胜负难料.

I'm doubtful where to go.

该往哪里去我心中无底.

The speaker was clearly playing to the gallery when he uttered so many doubtful jokes.

演说者讲了这么多似是而非的笑话,显然是迎合低级趣味.

questionable，doubtful，ambiguous，uncertain

这些形容词均含“怀疑的，不确定的”之意。

questionable通常指怀疑某行为是否恰当，或指有根有据的怀疑。

doubtful指对某个问题持积极怀疑的，有疑问的态度，强调缺乏确信。

ambiguous指因缺乏明确感或因为有各种不同的解释而值得怀疑。

uncertain多指因缺乏证据或了解而捉摸不定，也指因不能预料而不能作出选择。