Member of the Muslim brotherhood (4)
I believe the answer is:
limb
'member' is the definition.
(limb is a kind of member)
'of the muslim brotherhood' is the wordplay.
'of' indicates a hidden word.
'LIMB' is hidden within 'muslim brotherhood'.
(Other definitions for limb that I've seen before include "Wing, perhaps" , "Eg wing" , "Large tree branch" , "Part of body or branch of tree" , "Human's extension" .)