Preacher's ecclesiastic weapon (6)
I believe the answer is:
cannon
'weapon' is the definition.
(I know that cannon is a type of ordnance)
'preacher's ecclesiastic' is the wordplay.
'preacher's' shows a homophone (sound like) (as it might sound from someone preaching).
'ecclesiastic' becomes 'canon' (type of ecclesiastic or cleric).
'canon' is a homophone of 'CANNON'.
(Other definitions for cannon that I've seen before include "One of the big guns" , "mortar" , "Field gun" , "Big gun" , "Billiard shot in which player's ball hits the two others" .)