narthex.
1. Church vestibule, in Byzantine churches of two kinds: an esonarthex or inner narthex, between the outer porch and the body of the church proper separated from the nave and aisles by a wall, arcade, colonnade, or screen; or an exonarthex or outer narthex outside the main wall, sometimes also serving as the portico or part of the cloistered atrium or quadriporticus.

2. Medieval ante-church often with nave and aisles, sometimes referred to as a Galilee porch, as at Durham Cathedral.

Bibliography

Mango (1986);
J. Parker (1850);
D. Watkin (1986)

nar·thex / ˈnär[unvoicedth]eks/ • n. an antechamber, porch, or distinct area at the western entrance of some early Christian churches, separated off by a railing and used by catechumens, penitents, etc. ∎  an antechamber or large porch in a modern church.

narthex an antechamber, porch, or distinct area at the western entrance of some early Christian churches, separated off by a railing and used by catechumens, penitents, and others; an antechamber or large porch in a modern church. Recorded from the late 17th century, the word comes via Latin from Greek narthēx.

narthex (archit.) vestibule extending across the west end of a church. XVII. — L. narthēx — Gr. nárthēx giant fennel, stick, casket, narthex.