Agnomen
From Freepedia
An Agnomen is a nickname or an alias. It is not a pseudonym as it is a real name. But an agnomen is usually a name in addition and not a substitution for the real name. For example, Aristides "the Just" or "Iron" Mike Tyson.
Agnomens like "Britannicus" or "Nero" were used in ancient Rome to distinguish between similarly-named members of a family, or to honour of impressive accomplishments. For example, Coriolanus earned his from the capture of Coroli. See Roman naming convention.
