Back authoritarian (5)
I believe the answer is:
stern
I believe this clue is a double definition.
'back' is the first definition.
(I know that after part is a type of back)
'authoritarian' is the second definition.
(I've seen this in another clue)
(Other definitions for stern that I've seen before include "Old star" , "Dour" , "having a forbidding appearance" , "Severe and unremitting: area of a ship" , "Hard - back" .)