Sacred or inviolable (10)
I believe the answer is:
sacrosanct
This clue is a double definition.
'sacred' is the first definition.
(similar in meaning)
'inviolable' is the second definition.
(I know that inviolable can be written as sacrosanct)
(Other definitions for sacrosanct that I've seen before include "Too important to touch" , "Inviolable" , "above criticism" , "Unchallengeable" , "protected" .)