A head of department initially returned capital (4)
I believe the answer is:
doha
'capital' is the definition.
(capital of Qatar)
'a head of department initially returned' is the wordplay.
'initially' suggests taking the first letters.
'returned' is a reversal indicator.
The initial letters of 'head of department' is 'hod'.
'a'+'hod'='ahod'
'ahod' backwards is 'DOHA'.
(Other definitions for doha that I've seen before include "Capital of Qatar" , "Trade round" , "Gulf resort" .)