solemn

An event or situation that's solemn usually feels serious and respectful.

When people use the word "solemn" they often mean something like a funeral or a wedding, but not necessarily because it's happy. Think about it - when you go to a friend's grandma's funeral, everyone is there to be serious for a little while, show respect, and maybe cry. That can feel solemn. If someone says the atmosphere at their wedding was "solemn," they might mean that everything felt very important, like this moment would last forever.

Also, if you talk about something being a solemn promise or a solemn vow, it means people are making a strong and serious commitment to each other. It's not just a casual agreement - they're saying they'll really do this.