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.
To a degree, gentleman came to signify a man with an income derived from property, a legacy, or some other source, who was thus independently wealthy and did not need to work. [not verified in body] The term was particularly used of those who could not claim any other title or even the rank of esquire.