严肃 (yán sù): (ofบรรยากาศ ฯลฯ) solemn

At the memorial service, everyone wore black clothes with solemn expressions, and no one spoke a word in the entire hall.

During the interview, the examiner asked me solemnly why I chose this company, and I was so nervous that I could barely speak.

The doctor solemnly told us that the patient's condition was very serious and required immediate surgery.

The atmosphere in the classroom suddenly became very solemn because the homeroom teacher came in and announced an important piece of news.