Regret, Regretful, Contrition, Remorse
noun, な adjective, の adjective
A pain grudge is pain you feel from the grudge. I wish I could change my grudge. It is my regret.
つうこん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
痛恨のミスをしてしまい、彼にアドバイスしてもらうはめになりました。
I made a mistake I regret and ended up asking him for advice.