Coldness in church, not healthy (5)
I believe the answer is:
chill
'coldness' is the definition.
(chill is a kind of coldness)
'church not healthy' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'not healthy' becomes 'ill' (unwell or unhealthy).
'ch'+'ill'='CHILL'
'in' acts as a link.
(Other definitions for chill that I've seen before include "minor illness" , "A feeling of coldness" , "Make cool" , "Preserve by cold" , "Feverish cold; relax" .)