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 …

(Definition of questionable from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

If you say that something is questionable, you mean that it is not completely honest, reasonable, or acceptable.

Something that's questionable is uncertain or hard to believe. If a politician says things you doubt are true, you might describe his words as questionable.

1. of doubtful propriety, honesty, morality, etc.: questionable activities. 2. open to question; uncertain: questionable accuracy. 3. open to question as to being of the nature or value …

a statement of questionable accuracy. Synonyms: controvertible , dubious , dubitable , disputable , debatable open to question as to being of the nature or value suggested:

Definition of questionable adjective in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

There are nine meanings listed in OED's entry for the adjective questionable, five of which are labelled obsolete. See ‘Meaning & use’ for definitions, usage, and quotation evidence.

(Definition of questionable from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

[ + question word] It is highly questionable whether this drug has any benefits at all.