1) Able to be refuted 2) Alleged 3) Apocryphal 4) Contestable 5) Debatable 6) Doubtful 7) Dubious 8) Dubitable 9) Equivocal 10) Fishy 11) Funny 12) Impugnable 13) In question 14) In questionable taste 15) Open to question or dispute 16) Problematic 17) Problematical 18) Queer 19) Self-styled 20) Shady 1) Apocryphal 2) Arguable 3) Confutable 4) Confutative 5) Contestable 6) Debatable 7) Deniable 8) Disputable 9) Doubtful 10) Dubious 11) Dubitable 12) Equivocal 13) Fishy 14) Iffy 15) Impugnable 16) Moot 17) Problematic 18) Problematical 19) Refutable 20) Shady 21) Shaky 22) Suspect 23) Unlikely 24) Unreliable 
• (a.) Liable to question; subject to be doubted or called in question; problematical; doubtful; suspicious. • (a.) Admitting of being questioned; inviting, or seeming to invite, inquiry.
Ques'tion·a·ble adjective 1. Admitting of being questioned; inviting, or seeming to invite, inquiry. [ R.] « Thou com'st in such a questionable shape That I will speak to thee.» Shak. 2. Liable to question; subject to be doubted or called in question; prob...
[adj] - subject to question 2. [adj] - able to be refuted
questionable 1. Open to doubt or disagreement. 2. Not respectable or morally proper.
refutable adjective able to be refuted
of doubtful propriety, honesty, morality, respectability, etc.: questionable activities; in questionable taste. · open to question or dispute; doubtful or uncertain: a statement of questionable accuracy. · open to question as to being of the nature or value suggested: a questionable privilege.
subject to doubtful speculation