Rigid back end (5)
I believe the answer is:
stern
I believe this is a double definition.
'rigid' is the first definition.
(I've seen this in another clue)
'back end' is the second definition.
(I've seen this before)
(Other definitions for stern that I've seen before include "Forbidding, austere" , "Rigid" , "Rents out at rear of boat" , "at the back of the galley!" , "Strict; severe" .)