Severely criticise a god (3)
I believe the answer is:
pan
I believe this clue is a double definition.
'severely criticise' is the first definition.
(pan can mean to criticise heavily)
'a god' is the second definition.
(Pan is a Greek god)
(Other definitions for pan that I've seen before include "Toilet bowl" , "Sweep" , "Greek god of the mountains" , "Find fault with - container" , "'Mythical god, half man, half goat (3)'" .)