Courtliness is the quality of being graceful and polite in a slightly old, formal way — the manners people once linked with a royal court. It is a noun: not “he is courtliness,” but “he spoke with courtliness,” or “the courtliness of her manners.” It names the whole manner, not one please-and-thank-you. You will read it more than you will say it. Writers may like it (beautiful manners) or not trust it (manners so fine they feel like a mask). Though actually, at a real court, that grace and the game of pleasing a ruler often sat together. Today we mostly keep the nice surface: refined, careful politeness.