遗憾 (yí hàn): ความเสียใจ

We could have won this match, but in the end we lost because of my mistake. What a regret.

He felt very sorry that he couldn't attend his daughter's graduation ceremony because he was on a business trip abroad at the time.

She didn't study English well when she was young, and now she needs it for work, so she feels very regretful.

I heard that old bookstore closed last month, and many readers expressed their regret.

Regarding this accident, the company expresses deep regret and promises to strengthen safety measures.