Cook a revolutionary fellow (4)
I believe the answer is:
chef
'cook' is the definition.
(both can mean someone who cooks)
'a revolutionary fellow?' is the wordplay.
'a revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'fellow?' becomes 'f' (abbreviation - of a society etc.).
'che'+'f'='CHEF'
(Other definitions for chef that I've seen before include "one in the restaurant" , "Saucier" , "Originator of courses" , "Hotel cook" , "Kitchen head" .)