NICKNAME, a name given to a person in addition to his personal names, Christian and surname, either as a playful or familiar form of address or as a mark of ridicule, contempt or hatred. The Middle English form of the word, nekename, shows that it is a corruption of “an ekename” (i.e. “added” name; eke, earlier eche, from the root seen in Lat. augere, Gr. αὐξάνειν), and is therefore equivalent to the Lat. agnomen.
There is an interesting list of national nicknames in Notes and Queries, 9th series, 4, 212-214.