Source : Webster's Revised Unabridged Dictionary (1913)

Indefeasible \In`de*fea`si*ble\, a. [Pref. in- not + defeasible:
   cf. OF. indefaisable.]
   Not to be defeated; not defeasible; incapable of being
   annulled or made void; as, an indefeasible or title.

         That the king had a divine and an indefeasible right to
         the regal power.                         --Macaulay.

Source : WordNet®

indefeasible
     adj : not liable to being annulled or voided or undone; "an
           indefeasible right to freedom"; "an indefeasible claim
           to the title" [ant: {defeasible}]