This is the 9877th most frequent Japanese word.
許せる
"許せる" means "to be able to forgive."
The word "許せる" (can forgive/allow) is used here to express the ability or willingness to forgive the mentioned action.
この行動は私には許せると思います。
I think I can forgive this action.
In this sentence, "許せる" is used to depict justification for accepting the lateness due to a reason provided.
兄がまた遅刻したが、今回は許せる理由がある。
My brother was late again, but he has a reason that I can forgive this time.
Here, "許せる" emphasizes the difficulty or unwillingness to forgive due to the unacceptable nature of the words.