Regret about church gathering (5)
I believe the answer is:
ruche
'gathering' is the definition.
(I've seen this before)
'regret about church' is the wordplay.
'regret' becomes 'rue' (to rue something is to regret it).
'about' is an insertion indicator.
'church' becomes 'ch' (common abbreviation).
'rue' going around 'ch' is 'RUCHE'.
(Other definitions for ruche that I've seen before include "Decorative pleated strip" , "Pleated frill" , "Fabric frill or pleat" , "Strip of frilled lace" , "strip of lawn?" .)