Sacred chamber, outstanding (8)
I believe the answer is:
hallowed
'sacred' is the definition.
('hallowed' can be similar in meaning to 'sacred')
'chamber outstanding' is the wordplay.
'chamber' becomes 'hall' (I've seen this before).
'outstanding' becomes 'owed' ('owed' can be a synonym of 'outstanding').
'hall'+'owed'='HALLOWED'
(Other definitions for hallowed that I've seen before include "Sanctified" , "sacrosanct" , "Respected" , "Held holy" , "Revered" .)