Compare entertaining ambassador and cook (4)
I believe the answer is:
chef
'cook' is the definition.
(chef is a kind of cook)
'compare entertaining ambassador' is the wordplay.
'compare' becomes 'cf' ('cf.' can be a synonym of 'compare').
'entertaining' means one lot of letters goes inside another.
'ambassador' becomes 'he' (His or Her Excellency).
'cf' enclosing 'he' is 'CHEF'.
'and' is the link.
(Other definitions for chef that I've seen before include "Professional cook" , "Key kitchen worker" , "member of kitchen staff" , "One who prepares courses" , "responsible for courses" .)