Member of Muslim Brotherhood (4)
I believe the answer is:
limb
'member' is the definition.
(limb is a kind of member)
'of muslim brotherhood' is the wordplay.
'of' says the answer is hidden in the clue.
'LIMB' is hidden in the letters of 'muslim brotherhood'.
(Other definitions for limb that I've seen before include "Branch - member" , "Tentacle" , "Substantial branch from a tree trunk" , "as part of plane, say" , "Wing, perhaps" .)