Plain clothes expert in Moslem law (5)

I believe the answer is:

mufti

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This clue could be a double definition.

'plain clothes' is the first definition.
(I've seen this in another clue)

'expert in moslem law' is the second definition.
'mufti' can be an answer for 'expert' (Mufti is an example). I am not sure about the 'in moslem law' bit.

Can you help me to learn more?

(Other definitions for mufti that I've seen before include "Plain clothes - Muslim legal expert" , "Ordinary clothes" , "Non-military clothing" , "Plain clothes - Muslim law expert" , "Civilian clothing for a military person" .)

I've seen this clue in The Globe and Mail.

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