Religious community remains jolly about the onset of apocalypse (6)
I believe the answer is:
ashram
'religious community' is the definition.
(I've seen this in another clue)
'remains jolly about the onset of apocalypse' is the wordplay.
'remains' becomes 'ash' (remains of a fire).
'jolly' becomes 'rm'.
'about' means one lot of letters goes inside another.
'the onset of' suggests taking the first letters.
The initial letter of 'apocalypse' is 'a'.
'rm' enclosing 'a' is 'ram'.
'ash'+'ram'='ASHRAM'
(Other definitions for ashram that I've seen before include "Commune" , "Indian religious retreat" , "etreat" , "spiritual centre?" , "Hindu retreat location" .)