(a.) Not commutable; not capable of being exchanged with, or substituted for, another.

changeless constant immutable 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 unreturnable unsusceptible unvariable unvarying