serious

She gave me a serious look.

彼女は私に真剣な表情を向けた。

The accident was serious, causing major injuries.

その事故は深刻で、大きなけがを引き起こした。

Are you serious about moving to another country?

本気で他の国に引っ越すつもりなの？

His condition is serious and requires constant monitoring.

彼の状態は重く、常に監視が必要だ。