Cook some lunch effectively (4)
I believe the answer is:
chef
'cook' is the definition.
(both can mean someone who cooks)
'some lunch effectively' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'CHEF' is hidden within 'lunch effectively'.
(Other definitions for chef that I've seen before include "French master" , "Originator of courses" , "member of kitchen staff" , "one in the restaurant" , "responsible for courses" .)