Grave, solemn (7)
I believe the answer is:
serious
I believe this is a double definition.
'grave' is the first definition.
(I know that grave can be written as serious)
'solemn' is the second definition.
(similar in meaning)
(Other definitions for serious that I've seen before include "Earnest; vital" , "Not light or frivolous" , "Stern" , "Important - solemn" , "Solemn, thoughtful" .)