Relax, unwell after church (5)
I believe the answer is:
chill
'relax' is the definition.
(I've seen this before)
'unwell after church' is the wordplay.
'unwell' becomes 'ill' (similar in meaning).
'after' is a charade indicator (letters next to each other).
'church' becomes 'ch' (common abbreviation).
'ill' put after 'ch' is 'CHILL'.
(Other definitions for chill that I've seen before include "Slang injunction to relax - it's cold" , "Sensation of cold or dread" , "nip" , "minor illness" , "A feeling of coldness" .)