ambivalent

Compared meaning: not sure, doubtful, or having mixed feelings (adjective).

比较义项：对某事没有把握、心存怀疑或想法矛盾（形容词）。

• uncertain

  The most neutral, general word for not knowing something for sure — used about facts, decisions, or outcomes, often with about/whether; the default choice in formal or informal writing.

  最中性、通用的词，表示对某事没有把握——可用于事实、决定或结果，常与 about/whether 连用；是正式或非正式写作中的默认选择。

  Scientists are still uncertain about the long-term effects of the new drug.

  科学家们仍不确定这种新药会带来怎样的长期影响。

• unsure

  Very close to uncertain, but leans toward personal lack of confidence or not having made up one's mind; very common in everyday spoken English, more so than uncertain.

  与 uncertain 十分接近，但更侧重个人缺乏自信或尚未拿定主意；在日常口语中比 uncertain 更常见。

  I'm unsure whether I locked the front door before we left.

  我不确定离开前有没有锁好前门。

• dubious

  Implies doubt about whether something is true, honest or worthwhile — closer to suspicious or skeptical than merely lacking information; often used about explanations, offers or motives.

  表示怀疑某事是否真实、诚实或值得——比单纯缺乏信息更接近『怀疑、不信任』；常用于形容解释、提议或动机。

  He gave a dubious explanation for why he was late, and nobody believed him.

  他对自己迟到的解释很可疑，没有人相信他。

• ambivalent 本词

  Means having two conflicting feelings or opinions at once, not simply lacking certainty; more formal, often about decisions or relationships, and always implies an emotional pull both ways.

  表示同时存在两种矛盾的感受或看法，而不仅仅是没有把握；语气更正式，常用于描述决定或人际关系，并且总是暗示情感上正反两面的拉扯。

  She felt ambivalent about the promotion, excited about the pay but dreading the extra hours.

  她对这次升职感到矛盾，既为加薪感到兴奋，又害怕要多加班。

Uncertain, unsure, dubious, and ambivalent all mean not sure, but they differ. Uncertain and unsure just lack confidence. Dubious stresses doubt or distrust. Ambivalent means two opposite feelings at once, not just missing information. Dubious can also mean 'suspicious'; that meaning is not compared here.

这几个词在这个意义上都表示『不确定』，但语气和适用场合不同：uncertain 和 unsure 最接近，只是没有把握；dubious 更强调怀疑、不信任；ambivalent 则是心里同时有两种矛盾的感受，而不只是缺少信息。dubious 还可以形容人或事物本身『可疑、不可靠』（如 a dubious reputation），此处不作比较。