Religion I close violently (5)

I believe the answer is:

islam

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'religion' is the definition.
(Islam is a religion)

'i close violently' is the wordplay.
'close violently' becomes 'slam' (slamming is a kind of closing. I am not sure about the 'violently' bit.).
'i'+'slam'='ISLAM'

Can you help me to learn more?

(Other definitions for islam that I've seen before include "Faith with five pillars" , "Major world religion" , "Religion of the Koran" , "Religion based on teachings of Muhammad" , "Mohammed's religion" .)

I've seen this clue in the Sydney Morning Herald.

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