Cultivate fellow member (4)
I believe the answer is:
farm
'cultivate' is the definition.
(I know that farm is a more specific form of the action cultivate)
'fellow member' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'member' becomes 'arm' (member can mean a limb).
'f'+'arm'='FARM'
(Other definitions for farm that I've seen before include "agricultural centre" , "Old MacDonald's establishment" , "Smallholding" , "Agricultural establishment" , "Agricultural worker" .)