Stern and unsmiling (4)
I believe the answer is:
grim
'stern and unsmiling' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for grim that I've seen before include "Severe; horrible" , "Dour, forbidding" , "Stern, cruel" , "Dour and severe" , "Dark, depressing" .)