adj. 1 serious and dignified (a solemn occasion). 2 formal; accompanied by ceremony (a solemn oath). 3 mysteriously impressive. 4 (of a person) serious or cheerless in manner (looks rather solemn). 5 full of importance; weighty (a solemn warning). 6 grave, sober, deliberate; slow in movement or action (a solemn promise; solemn music). solemn mass = high mass (see MASS(2)). solemnly adv. solemness n.
[ ME f. OF solemne f. L sol(l)emnis customary, celebrated at a fixed date f. sollus entire ]