Rigid, tough (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)
'tough' is the second definition.
(I've seen this in another clue)
(Other definitions for stern that I've seen before include "Looking severe" , "Where sailors may be" , "Ship's rear" , "Strict, grimly serious" , "enforcing submission" .)