Narthex noun 1.in early Christian churches, a porch or portico at the west end for penitents and others not admitted to the church itself 2.any church vestibule leading to the nave Origin: LL(Ec) < LGr(Ec) narth?x < Gr, giant fennel: from a fancied resemblance of the porch to the hollow stem Webster's New World College Dictionary Copyright ? 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc. nar?thex (n?rˈthĕksˌ) noun 1.A portico or lobby of an early Christian or Byzantine church or basilica, originally separated from the nave by a railing or screen. 2.An entrance hall leading to the nave of a church.