- a dangerous operation.
- a grave illness.
- a grave situation.
- a life-threatening disease.
- a serious attempt to learn to ski.
- a serious book.
- a serious student of history.
- a serious turn of events.
- a serious wound.
- a serious young man.
- a severe case of pneumonia.
- are you serious or joking?.
- Don't be so serious!.
- gave me a serious look.
- good music.
- grievous bodily harm.
- marriage is a serious matter.
- raised serious objections to the proposal.
- the plan has a serious flaw.