Anyone can be nice. Many people have good manners. But gentility is that rare kind of graciousness that is handed down from one elegant generation to the next.
In the early 13th century, gentility described someone's social status, coming from the Old French word gentil, meaning "high-born, noble, of good family." Over time the word's meaning broadened to include those coming from a family whose members had a refined manner and an elegant way of expressing themselves — no title of nobility required, just as today anyone can be a gentleman (or woman).