(a.) Not to be defeated; not defeasible; incapable of being annulled or made void; as, an indefeasible or title.

certain changeless constant fated fateful immutable inalienable incommunicable incommutable inconvertible ineluctable inert inescapable inevasible inevitable inexorable inflexible insusceptible of change intransmutable invariable irresistible irretrievable irreversible irrevocable lasting necessary noble noncommunicable noncontagious noninfectious nonreturnable nonreversible permanent relentless resistless reverseless sure sure as death sure as fate unalterable unalterative unaltered unavoidable unchangeable unchanged unchanging uncontrollable undeflectable undeviating unimpartable unmodifiable unpreventable unremitting unrestorable unreturnable unstoppable unsusceptible unvariable unvarying unyielding