Formerly fit department head expired (7)
I believe the answer is:
exhaled
'expired' is the definition.
('exhale' can be a synonym of 'expire')
'formerly fit department head' is the wordplay.
'formerly' becomes 'ex' (prefix meaning former or onetime).
'fit' becomes 'hale' (both can mean healthy).
'head' suggests taking the first letters.
The first letter of 'department' is 'd'.
'ex'+'hale'+'d'='EXHALED'
(Other definitions for exhaled that I've seen before include "Sent out" , "Gave off" , "blown out" , "Breathed out" .)