A nobleman is a man in the highest social class who holds a title — duke, earl, baron, and names like that. The point is the title and the old class system, not only money. You meet it in history, fairy tales, and news about real titled families, especially in Britain. It is a fairly formal word. Though actually, students often hear noble and think “a good person”. That is another face of noble. Here noble means high-born. A rich businessman with no title is not a nobleman, even if he lives like one.