Villain heading off for part of church (4)
I believe the answer is:
Here is my best explanation:
'part of church' is the definition.
('nave' is part of 'church')
'villain heading off' is the subsidiary indication.
'villain' becomes 'knave' (knave is a kind of villain).
'heading off' means to remove the first letter.
'knave' with its first letter removed is 'nave'.
'for' is the link.
(Other definitions for nave that I've seen before include "Central space in church", "Part of a church sounds roguish", "Central part of church", "Central area in a church", "Church area", "Take no risks", "Wheel hub", "Main part of a church", "Main body of a church" and "Body of a church".)