1 serious, sober, reserved, grave, earnest, sedate, staid, taciturn; morose, morbid, mirthless, unsmiling, gloomy, sombre, grim; glum, long-faced, saturnine:
We observed a moment of solemn silence in memory of our fallen comrades. They knew from their father's solemn expression that something was wrong.
2 ceremonial, ritualistic, liturgical, religious, ecclesiastical, holy, divine, sacred, hallowed, sacramental, reverential, devotional:
We attended a solemn service to celebrate the return of the hostages.
3 ceremonious, ritual, formal, dignified, stately, grand, august, imposing, impressive, awe-inspiring, awesome, important, momentous:
The Trobriand islanders regarded the rights of passage as most solemn.