Section within department (4)
I believe the answer is:
part
'section' is the definition.
(I know that section is a more specific form of part)
'within department' is the wordplay.
'within' indicates a hidden word.
'PART' is hidden within 'department'.
(Other definitions for part that I've seen before include "Divide; role" , "Component; divide" , "Bit - leave" , "Member" , "goodbye" .)