THESAURUS
unreturnable
changeless, constant, immutable, incommutable, inconvertible, indefeasible, inert, insusceptible of change, intransmutable, invariable, irretrievable, irreversible, irrevocable, lasting, noble, nonreturnable, nonreversible, permanent, reverseless, unalterable, unalterative, unaltered, unchangeable, unchanged, unchanging, undeflectable, undeviating, unmodifiable, unremitting, unrestorable, unsusceptible, unvariable, unvarying
