Preacher gave silent order (10)
I believe the answer is:
evangelist
'preacher' is the definition.
(an evangelist spreads or preaches their religion)
'gave silent order' is the wordplay.
'order' indicates an anagram.
'gave'+'silent'='gavesilent'
'gavesilent' is an anagram of 'EVANGELIST'.
(Other definitions for evangelist that I've seen before include "Zealous believer" , "Zealous advocate" , "Gospel writer" , "Preacher" , "Mark for one" .)