Hard back (5)
I believe the answer is:
stern
I believe this is a double definition.
'hard' is the first definition.
(I've seen this in another clue)
'back' is the second definition.
(stern means the back of a boat)
(Other definitions for stern that I've seen before include "Rear; severe, serious" , "Grim; severe" , "Strict, grimly serious" , "having a forbidding appearance" , "Severe, forbidding" .)