Seneca Syllabification: (Sen·e·ca)Pronunciation: /ˈsenəkə/Definition of Seneca noun (plural same or Senecas) 1a member of an American Indian people that was one of the Five Nations. 2the Iroquoian language of the Seneca. adjective relating to the Seneca or their language. Origin:via Dutch from AlgonquianSeneca in other Oxford dictionaries Definition of Seneca in the British & World English dictionary