See Californian policeman retiring after a revelation (10)
I believe the answer is:
apocalypse
'revelation' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for apocalypse that I've seen before include "Catastrophic event" , "World's end" , "End of the world" , "sacred book" , "This last book" .)