Source : Webster's Revised Unabridged Dictionary (1913)

Unquestionable \Un*ques"tion*a*ble\, a.
   1. Not questionable; as, an unquestionable title.

   2. Not inviting questions or conversation. [R.] --Shak. --
      {Un*ques"tion*a*bly}, adv.

Source : WordNet®

unquestionably
     adv 1: without question; "Fred Winter is unquestionably the jockey
            to follow"; "they hired unimpeachably first-rate
            faculty members" [syn: {unimpeachably}]
     2: without question and beyond doubt; "it was decidedly too
        expensive"; "she told him off in spades"; "by all odds
        they should win" [syn: {decidedly}, {emphatically}, {definitely},
         {in spades}, {by all odds}]