What is a gentleman?

A gentleman is a gentle man. In this connection, the word “gentle” means “noble”, as it does in the phrase “of gentle birth”. So, originally, a gentleman was one who, by birth and training, belonged to the upper classes. He was of noble blood. Then, because the social manners of the upper classes were refined, as compared with those of the lower classes, anyone who knew how to behave in polite society came to be called a gentleman. So gentlemanliness came to refer to outward behavior. A man who behaved like a gentleman was a gentle man.