Ism
Principle, Doctrine
noun, suffix
The main cause behind someone's righteousness is usually what isms, principles or doctrines they believe in. Buddhism, Shintoism, socialism, communism, you name it. If you believe in one of those it's the main driving factor behind what you believe righteousness to be.
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.
グチをこぼしても何も解決しないので、私はグチを言わない主義なんです。
Grumbling won't solve anything, so I have a policy of never complaining.
オレは語尾に主義が付いている言葉は使わない主義なんだよ！
One of my principles is that I don't use words ending in -ism.
フグは肉を食べないよ。菜食主義者だからさ。
Fugu doesn’t eat meat. He’s a vegetarian.