The term 'Hatfields or McCoys' refers to two famous American families who were involved in a long-running feud in the late 19th century. The crossword solution for this term is 'CLAN, ' which is an appropriate description of both families. A CLAN is a group of people who are related by blood or marriage and share a common ancestor. The Hatfields and McCoys were two large extended families who had a long-standing rivalry that eventually led to violence.