Religious leader raised in slum, a missionary (4)
I believe the answer is:
imam
'religious leader' is the definition.
(I've seen this before)
'raised in slum a missionary' is the wordplay.
'raised' says the letters should be written in reverse.
'in' indicates a hidden word.
'mami' is hidden in the letters of 'slum a missionary'.
'mami' back-to-front is 'IMAM'.
(Other definitions for imam that I've seen before include "Islamic religious leader" , "Authority on Islamic doctrine and law" , "man of prayer" , "Caliph" , "Islamic prayer leader" .)