Source : Webster's Revised Unabridged Dictionary (1913)

Questionable \Ques"tion*a*ble\, a.
   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; problematical; doubtful; suspicious.

            It is questionable whether Galen ever saw the
            dissection of a human body.T.         -- Baker.

   Syn: Disputable; debatable; uncertain; doubtful;
        problematical; suspicious.

Source : WordNet®

questionable
     adj 1: subject to question; "questionable motives"; "a questionable
            reputation"; "a fire of questionable origin" [ant: {unquestionable}]
     2: able to be refuted [syn: {refutable}, {confutable}, {confutative}]