I harshly criticise one of the big religions (5)

I believe the answer is:

islam

'one of the big religions' is the definition.
(Islam is a world religion)

'i harshly criticise' is the wordplay.
'harshly criticise' becomes 'slam' (to slam is to criticise or condemn).
'i'+'slam'='ISLAM'

(Other definitions for islam that I've seen before include "Religion based on Muhammad's teachings" , "Belief" , "Mohammed's religion" , "Creed" , "Monotheistic religion" .)

I've seen this clue in The Independent.

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