(a.) Not convertible; not capable of being transmuted, changed into, or exchanged for, something else; as, one metal is inconvertible into another; bank notes are sometimes inconvertible into specie.

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