Charity is closer to ใจบุญ (jai-bun) than น้ำใจ (nam-jai).
A mixture of "act of kindness" and "good will" would be a more fitting translation, but the interesting part here is that "sportmanship" is also considered an act of น้ำใจ (น้ำใจนักกีฬา nam-jai nak-kee-la or literally. sportman's nam-jai).
We also have a word เสียน้ำใจ (sia-nam-jai) for when our nam-jai ended up as a waste, or for when the other party is being ungrateful for the kindness that's being given, and also เลี้ยงน้ำใจ (leang-nam-jai) for when you're doing/accepting nam-jai for the sake of not making the other party sia-nam-jai.
In the King James Bible you have lovingkindness but I guess that might be a mistranslation of the Hebrew checed which literally means "covenant loyalty." But I feel like lovingkindness even if it was originally mistranslated has the same connotation as nam-jai.
A mixture of "act of kindness" and "good will" would be a more fitting translation, but the interesting part here is that "sportmanship" is also considered an act of น้ำใจ (น้ำใจนักกีฬา nam-jai nak-kee-la or literally. sportman's nam-jai).
We also have a word เสียน้ำใจ (sia-nam-jai) for when our nam-jai ended up as a waste, or for when the other party is being ungrateful for the kindness that's being given, and also เลี้ยงน้ำใจ (leang-nam-jai) for when you're doing/accepting nam-jai for the sake of not making the other party sia-nam-jai.