1) недостоверный 2) неопределённый, сомнительный
прилагательное 1) сомневающийся, нерешительный, полный сомнений Например: They were doubtful whether the new engine will be any better. — Они сомневались, что новый двигатель будет чем-то лучше. 2) вызывающий сомнения, опасения; сомнительный Например: It is doubtful that they ever knew what had happened. — Вряд ли им вообще было известно, что случилось. 3) сомнительного свойства, качества Например: doubtful reputation — сомнительная репутация 4) неопределенный, неясный, сомнительный Например: The result of the Presidential elections remains doubtful. — Результаты президентских выборов остаются неясными. Синоним(ы): questionable, uncertain, problematic Антоним(ы): clear, confident, decided, definite, sure
adjective 1. giving rise to doubt; open to question Example: it is doubtful that they ever knew what happened 2. a. lacking a definite opinion, conviction, or determination Example: they were doubtful about the advantages of the new system b. uncertain in outcome; undecided Example: the outcome of the election remains doubtful 3. marked by qualities that raise doubts about worth, honesty, or validity Example: of doubtful repute • doubtfully adverb • doubtfulness noun Synonyms: doubtful, dubious, problematic, questionable mean not affording assurance of the worth, soundness, or certainty of something. doubtful implies little more than a lack of conviction or certainty Example: doubtful about whether I said the right thing. dubious stresses suspicion, mistrust, or hesitation Example: dubious about the practicality of the scheme. problematic applies especially to things whose existence, meaning, fulfillment, or realization is highly uncertain Example: whether the project will ever be finished is problematic. questionable may imply no more than the existence of doubt but usually suggests that the suspicions are well-grounded Example: a man of questionable honesty.