Demanding back… (5)
I believe the answer is:
stern
This clue is a double definition.
'demanding' is the first definition.
(similar in meaning)
'back' is the second definition.
(stern means the back of a boat)
(Other definitions for stern that I've seen before include "Severe, demanding" , "Severe in the rear of the ship?" , "Forbidding in aspect" , "Rigid" , "Unsmiling" .)