Islamic order's oil happened to be endless (5)

I believe the answer is:

fatwa

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'islamic order's oil happened to be endless' is the definition.
I can't judge whether this defines the answer.

'oil happened to be endless' is the wordplay.
'oil' becomes 'fat'.
'happened to' becomes 'w' (I am not sure about this - if you are sure you should believe this answer much more).
'be' becomes 'am'.
'endless' means to remove the last letter.
'am' with its final letter taken off is 'a'.
'fat'+'w'+'a'='FATWA'

Can you help me to learn more?

(Other definitions for fatwa that I've seen before include "Islamic opinion" , "Authoritative ruling (Islam)" , "Islamic sentence as on Salman Rushdie" , "Formal ruling on a point of Islamic law" , "Muslim decree or formal legal judgement" .)

I've seen this clue in The Times.

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