Sombre accent (5)
I believe the answer is:
grave
I believe this is a double definition.
'sombre' is the first definition.
(I've seen this before)
'accent' is the second definition.
(grave is a kind of accent)
(Other definitions for grave that I've seen before include "Dignified" , "Grim-faced" , "Solemn, serious" , "Serious in cemetery?" , "In which to lay a corpse" .)