Because of the limited nature of the Latin praenomen, the cognomen developed to distinguish branches of the family from one another, and occasionally, to highlight an individual's achievement, typically in warfare.
Some cognomina were hereditary (such as Caesar among a branch of the Julii, Brutus and Silanus among the Junii, or Pilius and Metellus among the Caecilii): others tended to be individual.
[2] In present academic context, many prominent ancient Romans are referred to by only their cognomen; for example, Cicero (from cicer "chickpea") serves as a shorthand for Marcus Tullius Cicero, and Caesar for Gaius Julius Caesar.
According to the 2012 edition of the Random House Dictionary, cognomen can mean a "surname" or "any name, especially a nickname".
The term "cognomen" can also be applied to cultures with a clan structure and naming conventions comparable to those of Ancient Rome; thus, hereditary "cognomina" have been described as in use among the Xhosa (Iziduko), the Yoruba (Oriki), and the Zulu (Izibongo).