Jack’s part of church, by the sound of it (5)
I believe the answer is:
knave
'jack's' is the definition.
(knave can mean a jack playing card)
'part of church by the sound of it' is the wordplay.
'part of church' becomes 'nave' ('nave' is part of 'church').
'by the sound of it' shows a homophone (sound like).
'nave' sounds like 'KNAVE'.
(Other definitions for knave that I've seen before include "Jack (card); base fellow" , "Jack - rotter" , "cheat of old" , "A rogue as in playing cards" , "Jack - rogue" .)