Plain clothes (5)
I believe the answer is:
mufti
'plain clothes' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mufti that I've seen before include "Plain clothes - Muslim legal expert" , "Non-military clothing" , "Civilian clothing; Muslim legal expert" , "Civilian clothing for a military person" , "Civilian dress (for serviceman)" .)