agnomen

< /ægˈnɒm ə nə/.

1. an additional, fourth name given to a person by the ancient Romans in allusion to some achievement or other circumstance, as “Africanus” in “Publius Cornelius Scipio Africanus.”Compare cognomen(def 3).
2. a nickname.

noun plural -nomina (-ˈnɒmɪnə)

1. the fourth name or second cognomen occasionally acquired by an ancient RomanSee also cognomen, nomen, praenomen
2. another word for nickname