1A na-adjective/noun meaning serious, severe, or grave — used when a situation, problem, illness, or crisis has deep, significant negative consequences.
その国の経済は深刻な問題を抱えている。
That country's economy is facing serious problems.
環境汚染が深刻になっている地域がある。
There are regions where environmental pollution has become severe.
彼の症状は深刻で、すぐに治療が必要だ。
His condition is serious and requires immediate treatment.
彼女は深刻な顔つきで相談してきた。
She came to me for advice with a serious expression on her face.