Stern, forbidding (4)
I believe the answer is:
grim
I believe this is a double definition.
'stern' is the first definition.
(I know that stern can be written as grim)
'forbidding' is the second definition.
(I know that forbidding can be written as grim)
(Other definitions for grim that I've seen before include "Dour, forbidding" , "Dreadful" , "Dismal, dour" , "Tight-lipped and foreboding" , "Very serious/gloomy" .)