Antonomasia
ANTONOMASIA, in rhetoric, the Greek term for a substitution of any epithet or phrase for a proper name; as "Pelides," or "the son of Peleus," for Achilles; "the Stagirite" for Aristotle; "the author of Paradise Lost" for Milton; "the little corporal" for Napoleon I.; "Macedonia's madman" for Alexander the Great, etc. etc. The opposite substitution of a proper name for some generic term is also sometimes called antonomasia; as "a Cicero" for an orator.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)