The Greek word literally means "a small case."
A vestibule, usually a wide one across the front (west end) of a church, considered as a part of the church nave. In the early ages catechumens, candidates for baptism, and penitents occupied the narthex.
Dictionary of church terms. — St. GEORGE'S COPTIC ORTHODOX CHURCH SPORTING - ALEXANDRIA EGYPT. Fr. Tadros Yacoub Maiaty.