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.
For other uses, see MR. Mister, usually written in its abbreviated form Mr. (US) or Mr (US & UK), is a commonly used English honorific for men under the rank of knighthood. The title derived from earlier forms of master, as the equivalent female titles Mrs, Miss, and Ms all derived from earlier forms of mistress.