I bought an obligatory box of chocolates for my father in law.
You have righteousness and then a reason behind it, at least in your own mind. This is your sense of duty. And it really is a "sense" in a way, too. You just feel it. It's not an actual thing that is tangible. It is your own personal reason for this righteousness.
This word can also mean in-law like your mother-in-law, because they're your mother in the social obligation sense only, not by blood.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.