Synonyms serious
serious
grave ▪ earnest ▪ solemn
These words all describe somebody who thinks and behaves carefully and sensibly, but often without much joy or laughter.
serious thinking about things in a careful and sensible way; not laughing about something:
He’s not really a very serious person.
Be serious for a moment; this is important.
grave (rather formal) (of a person) serious in manner, as if something sad, important, or worrying has just happened:
He looked very grave as he entered the room.
earnest serious and sincere:
The earnest young doctor answered all our questions.
solemn looking or sounding very serious, without smiling; done or said in a very serious and sincere way:
Her expression grew solemn.
I made a solemn promise that I would return.
Patterns
a(n) serious/grave/earnest/solemn expression/face
a serious/solemn mood/atmosphere