Heard Jack in part of church (4)
I believe the answer is:
nave
'part of church' is the definition.
('nave' is part of 'church')
'heard jack' is the wordplay.
'heard' indicates a 'sounds like' (homophone) clue.
'jack' becomes 'knave' ('knave' can be a synonym of 'jack').
'knave' is a homophone of 'NAVE'.
'in' is the link.
(Other definitions for nave that I've seen before include "Main part of a church" , "The hub of a wheel, or body of church" , "Middle of wheel" , "Take no risks" , "Part of a church sounds roguish" .)