THESAURUS
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