Chalcedonian
Concise Oxford English Dictionary © 2008 Oxford University Press:
Chalcedonian /ˌkalsɪˈdəʊnɪən/
▶adjective relating to the ecumenical council of the Christian Church, held at Chalcedon in ancient Bithynia in 451, which affirmed the dual but united nature of Christ as god and man.
'Chalcedonian' also found in these Oxford entries:

