Solemn, not inclined to flippancy (7)
I believe the answer is:
serious
(Other definitions for serious that I've seen before include "Earnest, sincere" , "Earnest - important" , "Stern" , "Earnest; vital" , "Not light or frivolous" .)
I believe the answer is:
serious
(Other definitions for serious that I've seen before include "Earnest, sincere" , "Earnest - important" , "Stern" , "Earnest; vital" , "Not light or frivolous" .)