Wordnet 3.0
ADJECTIVE (1)
1. 
 not capable of being changed into something else; 
- Example: "the alchemists were unable to accept the inconvertible nature of elemental metals"[syn: inconvertible, untransmutable]
The Collaborative International Dictionary of English v.0.48:
Untransmutable \Untransmutable\
   See transmutable.
WordNet (r) 3.0 (2006):
untransmutable
    adj 1: not capable of being changed into something else; "the
           alchemists were unable to accept the inconvertible nature
           of elemental metals" [syn: inconvertible,
           untransmutable]