The adjective somber means an appearance or feeling of being sad or serious.

Synonyms are depressing, dark, gloomy, or melancholy.

The word origins from French (1730) sombre meaning “dark, gloomy”, and Old French (14th century) sombre (also sources from Late Latin subumbrare meaning “to shadow”). It comes from sub meaning “under” plus umbra meaning “shade, shadow“.

Mary’s mood remained somber throughout the ceremony.

She knew right then that something’s wrong when she met his somber gaze.

The somber note in his voice made everyone worried.