Revolutionary with fish head to cook (4)
I believe the answer is:
chef
'cook' is the definition.
(chef is a kind of cook)
'revolutionary with fish head' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'with' means one lot of letters go next to another.
'head' says to take the initial letters.
The first letter of 'fish' is 'f'.
'che'+'f'='CHEF'
'to' acts as a link.
(Other definitions for chef that I've seen before include "Head cook in a restaurant" , "member of kitchen staff" , "Professional cook" , "responsible for courses" , "One who prepares courses" .)