Source : Webster's Revised Unabridged Dictionary (1913)

Undeterminable \Un`de*ter"mi*na*ble\, a.
   Not determinable; indeterminable. --Locke.

Source : WordNet®

undeterminable
     adj : not capable of being definitely decided or ascertained [syn:
            {indeterminable}] [ant: {determinable}]