Indefeasible
ahd-5
adjective.
That cannot be annulled or made void.
The Century Dictionary and Cyclopedia
Not defeasible; not to be defeated or made void; that cannot be set aside or overcome.
the GNU version of the Collaborative International Dictionary of English
adjective.
Not to be defeated; not defeasible; incapable of being annulled or made void.
Wiktionary, Creative Commons Attribution/Share-Alike License
adjective.
not liable to being annulled or declared void.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
adjective.
not liable to being annulled or voided or undone