Put your damn dictionaries away right now or you’ll never learn anything!
In D&D, Good doesn’t mean “morally righteous.” Nor does it mean “pious” or any of a thousand other definitions. Capitol G “Good” means that you care about the well-being of others more than your own. That’s it, straight and true. It doesn’t mean you refuse to hurt people (code of conduct), it doesn’t mean you serve the church (behavior), and it doesn’t mean you have to fight Evil (code of conduct).
Sir William, Paladin of the Order, a seventh level Lawful Good fighter, is best friends with Bostwick, the Chaotic Evil “Cleric of Death.” They’ve been best friends since they were children, and the nations they rule are the two most powerful nations on the map because they’ve been working together.