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.
gentleman (plural gentlemen) ( 1 chiefly historical) A man of gentle but not noble birth, particularly a man of means (originally ownership of property) who does not work for a living but has no official status in a peerage; (Britain law) an armiferous man ranking below a knight.