Source : Webster's Revised Unabridged Dictionary (1913)

Unconquerable \Un*con"quer*a*ble\, a.
   Not conquerable; indomitable. -- {Un*con"quer*a*bly}, adv.

Source : WordNet®

unconquerable
     adj 1: not capable of being conquered or vanquished or overcome; "a
            tribute to his courage...and his unconquerable will"-
            R.E.Danielson; "faced unconquerable difficulties"
            [ant: {conquerable}]
     2: incapable of being surmounted or excelled; "insuperable
        odds"; "insuperable heroes" [syn: {insuperable}]