a portico at the west end of a basilica or church, esp one that is at right angles to the nave
2.
a rectangular entrance hall between the porch and nave of a church
[C17: via Latin from Medieval Greek: enclosed porch, enclosure (earlier: box), from Greek narthēx giant fennel, the stems of which were used to make boxes]
"porch at the end of early churches" (used by penitents not admitted to the body of the church), 1673, from Late Gk. narthex, from Gk. narthex "giant fennel," of unknown origin. The architectural feature so called from fancied resemblance of porch to a hollow stem. The word also was used in Gk. to mean