Novitiate, one they ordered to keep quiet (8)
I believe the answer is:
neophyte
'novitiate' is the definition.
(thesaurus)
'one they ordered to keep quiet' is the wordplay.
'ordered' indicates an anagram.
'to keep' means one lot of letters goes inside another.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'one'+'they'='onethey'
'onethey' with letters rearranged gives 'neohyte'.
'neohyte' enclosing 'p' is 'NEOPHYTE'.
(Other definitions for neophyte that I've seen before include "newcomer on the scene" , "One's just taken orders" , "Beginner, novice" , "Recent convert" , "They open for a new convert" .)