nomen Syllabification: (no·men)Pronunciation: /ˈnōmen/Definition of nomen noun Roman History the second personal name of a citizen of ancient Rome, indicating the gens to which he belonged, for example, Marcus Tullius Cicero. Compare with cognomen, praenomen, agnomen.Origin:Latin, literally 'name'nomen in other Oxford dictionaries Definition of nomen in the British & World English dictionary