Synonyms: inconvertible, untransmutable
Definition: not capable of being changed into something else
Usage: the alchemists were unable to accept the inconvertible nature of elemental metals
Similar words: incommutable
Definition: not subject to alteration or change
Synonyms: inconvertible, unconvertible, unexchangeable
Definition: used especially of currencies; incapable of being exchanged for or replaced by another currency of equal value
Similar words: irredeemable
Definition: (of paper money) not convertible into coin at the pleasure of the holder