antonomasia

英 [,æntənə'meɪzɪə; æn,tɒnə-] 美[,æntəno'meʒɪə]

antonomasia (n.): use of an epithet for a proper name (or vice versa; as in His Holiness for the name of a pope), 1580s, from Latin, from Greek antonomasia, from antonomazein "to name instead, call by a new name," from anti "instead" (see anti-) + onomazein "to name," from onoma "name" (see name (n.)).