solemn

serious and formal, especially in a way that is slightly frightening or impressive

solemne, serio, grave

• a solemn occasion/moment

Collocations solemn ceremony · solemn silence

• The wedding was a very solemn occasion.

  La boda fue una ocasión muy solemne.

serious and sincere, especially when making a promise or an important decision

solemne, serio, formal

• a solemn vow/promise

Collocations solemn promise · solemn oath

• He made a solemn promise to never lie again.

  Hizo un juramento solemne de no mentir nunca más.