Novice in religious order, one they ordered to keep quiet (8)
I believe the answer is:
neophyte
'novice in religious order' is the definition.
(neophyte can mean a religious novice)
'one they ordered to keep quiet' is the wordplay.
'ordered' indicates an anagram.
'to keep' is an insertion indicator.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'one'+'they'='onethey'
'onethey' with letters rearranged gives 'neohyte'.
'neohyte' placed around 'p' is 'NEOPHYTE'.
(Other definitions for neophyte that I've seen before include "They open for a new convert" , "raw recruit" , "Newcomer, starter" , "newcomer on the scene" , "Beginner, novice" .)