Solemn (7)
'solemn' is the definition.
(similar in meaning)
This is the entire clue.
(Other definitions for serious that I've seen before include "Solemn, thoughtful" , "Earnest; vital" , "Important - solemn" , "Earnest - important" , "Stern" .)
'solemn' is the definition.
(grave can mean solemn or serious)
This is the entire clue.
(Other definitions for grave that I've seen before include "Last resting place" , "In which to lay a corpse" , "Sleek, black" , "Solemn; tomb" , "Dignified" .)