Definition of "cognomen"

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

"Five hundred years or more afterwards, the family migrated to Rome under circumstances of which no trace remains, and here, probably with the idea of preserving the idea of vengeance which we find set out in the name of Tisisthenes, they appear to have pretty regularly assumed the cognomen of Vindex, or Avenger."

1886 October – 1887 January, H[enry] Rider Haggard, She: A History of Adventure, London: Longmans, Green, and Co., published 1887

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

Her husband was evidently a sensible man, and he might have given his wife a little more sense than she could have derived from her downright father and her silly mother-in-law, who were really as great a pair of noodles as ever were exhibited in the pages of a modern novel, under the cognomen of "amiable rustics."

1838 (date written), L[etitia] E[lizabeth] L[andon], chapter XVIII, in Lady Anne Granard; or, Keeping up Appearances. […], volume I, London: Henry Colburn, […], published 1842, page 237

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 December 23, Dragons' Den, spoken by Evan Davis