cognomen

Etymology

From Latin cognōmen, from con- (“with”) + nōmen (“name; family name”).

noun

1. (historical) A personal epithet or clan name added to the given name and family name of Ancient Romans.
   Julius Caesar's actual name was Gaius Iulius Caesar. Gaius was his praenomen or forename, Iulius his nomen or surname, and Caesar his cognomen, denoting which part of the Iulius family he belonged to.
   Roman tradition suggests that he might also have had the cognomen Octavian to indicate his biological family. 2007, David Potter, chapter 1, in The Emperors of Rome, page 36
2. (literary or humorous) Synonym of nickname, any epithet used similar to the Roman cognomina.
   In this by-place of nature, there abode, in a remote period of American history, that is to say, some thirty years since, a worthy wight of the name of Ichabod Crane; who sojourned, or, as he expressed it, "tarried," in Sleepy Hollow[…]. The cognomen of Crane was not inapplicable to his person. 1820, Washington Irving, The Legend of Sleepy Hollow, published 1864
3. (literary or humorous, uncommon) Synonym of surname, a family name.
   What's in a name? Well, to the Dragons, it would seem rather a lot, as they've tonight committed their cash to personalised products and to the man with the most famous cognomen in confectionery. I'll leave you to look that one up. 2018-12-23, Dragons' Den, spoken by Evan Davis