grave problems, situations, or worries are very great or bad [↪ serious]:
Matthew's life is in grave danger.
The report expressed grave concern over the technicians' lack of training.
I have grave doubts about his ability.
The situation is becoming very grave.
looking or sounding quiet and serious, especially because something important or worrying has happened [= sombre]:
Turnbull's face was grave as he told them about the accident.
—gravely adverb:➔ gravity
Adam nodded gravely.
We are gravely concerned (=very concerned) about these developments.