Autocrat reversed corruption at police department (8)
I believe the answer is:
dictator
'autocrat' is the definition.
(thesaurus)
'reversed corruption at police department' is the wordplay.
'reversed' says the letters should be written in reverse.
'corruption' becomes 'rot' (I've seen this before).
'police department' becomes 'cid' (I've seen this in other clues).
'rot'+'at'+'cid'='rotatcid'
'rotatcid' in reverse letter order is 'DICTATOR'.
(Other definitions for dictator that I've seen before include "Despot" , "Tyrant like Mussolini or Franco" , "Eg, Stalin" , "Absolute ruler (Great in Chaplin film)" , "Such as Saddam Hussein" .)