solemn
1 earnest, glum, grave, portentous, sedate, serious, sober, staid, thoughtful
2 august, awe-inspiring, ceremonial, ceremonious, dignified, formal, grand, grave, imposing, impressive, majestic, momentous, stately
3 devotional, hallowed, holy, religious, reverential, ritual, sacred, sanctified, venerable
Antonyms
1 & 2 bright, cheerful, chirpy (informal) comical, frivolous, genial, happy, informal, jovial, light-hearted, merry, relaxed, unceremonious
3 irreligious, irreverent, unholy