Inventor, head of department, is seen in time (6)
I believe the answer is:
edison
'inventor' is the definition.
(Edison is an example)
'head of department is seen in time' is the wordplay.
'head of' says to take the initial letters.
'seen in' is an insertion indicator.
'time' becomes 'eon' (eon is a kind of time**).
The initial letter of 'department' is 'd'.
'd'+'is'='dis'
'dis' going within 'eon' is 'EDISON'.
(Other definitions for edison that I've seen before include "Prolific inventor" , "scientist" , "Inventor of the carbon filament lamp, d. 1931" , "US inventor of phonograph, electric light etc." , "He came up with microphone" .)