Leader deceived about office finally (4)
I believe the answer is:
head
'leader' is the definition.
(I know that head is a type of leader)
'deceived about office finally' is the wordplay.
'deceived' becomes 'had' (I've seen this in another clue).
'about' indicates putting letters inside.
'finally' says to take the final letters.
The final letter of 'office' is 'e'.
'had' going around 'e' is 'HEAD'.
(Other definitions for head that I've seen before include "River or stream source" , "Cranium" , "Beer foam; front" , "Source of river, leader" , "Promontory; foam" .)