Antonomasia

Part of speech: noun (n.)

The use of some epithet or the name of some office, dignity, or the like, instead of the proper name of the person; as when his majesty is used for a king, or when, instead of Aristotle, we say, the philosopher; or, conversely, the use of a proper name instead of an appellative, as when a wise man is called a Solomon, or an eminent orator a Cicero.