To mourn or lament (often used about a person's death or misfortune).
彼は突然の訃報を聞いて深く悔やんだ。
He deeply mourned when he heard the sudden news of the death.
家族は事故で亡くなった人を悔やんでいた。
The family was mourning the person who died in the accident.
彼女は静かに手を合わせて故人を悔やんだ。
She quietly put her hands together and lamented the deceased.
To feel sorry for, to regret, or to repent (a decision or action).
試験に落ちたことを今でも悔やんでいる。
I still regret having failed the exam.
あの時あんなことを言ったことを悔やんで、謝りに行った。
Regretting that he said such things back then, he went to apologize.
後で悔やんでも遅いよ。
It will be too late to regret it later.