The definition of an adjective is a part of speech that is used to describe a noun. Red, tall, better and fast are all examples of adjectives.
In modern parlance, a gentleman (from gentle + man, translating the Old French gentilz hom) is any man of good, courteous conduct. A gentleman may also simply be a polite term for any man, as in indications of gender-separated facilities, or as a sign of the speaker's own courtesy when addressing others. The modern female equivalent is lady.
The Gentleman is always truthful and sincere; will not agree for the sake of complaisance or out of weakness ; will not pass over that of which he disapproves. He has a clear soul, and a fearless, straightforward tongue. On the other hand he is not blunt and rude.