Inviolable (10)
I believe the answer is:
sacrosanct
'inviolable' is the definition.
(I know that inviolable can be written as sacrosanct)
This is the entire clue.
(Other definitions for sacrosanct that I've seen before include "Too valuable to be changed" , "protected" , "Too valuable to touch" , "above criticism" , "Co-stars can (anag.)" .)