Source : Webster's Revised Unabridged Dictionary (1913)

Redoubtable \Re*doubt"a*ble\ (-?*b'l), a. [F. redoutable,
   formerly also spelt redoubtable.]
   Formidable; dread; terrible to foes; as, a redoubtable hero;
   hence, valiant; -- often in contempt or burlesque. [Written
   also {redoutable}.]

Source : WordNet®

redoubtable
     adj 1: inspiring fear; "the formidable prospect of major surgery";
            "a tougher and more redoubtable adversary than the
            heel-clicking, jackbooted fanatic"- G.H.Johnston;
            "something unnerving and prisonlike about high gray
            wall" [syn: {formidable}, {unnerving}]
     2: having or worthy of pride; "redoubtable scholar of the
        Renaissance"; "born of a redoubtable family" [syn: {glorious},
         {illustrious}, {respected}]