Narthex n. : A tall umbelliferous plant (Ferula communis). See Giant fennel, under Fennel.

Narthex n. : The portico in front of ancient churches; sometimes, the atrium or outer court surrounded by ambulatories; -- used, generally, for any vestibule, lobby, or outer porch, leading to the nave of a church.

Example:
I dont get what the Narthex (in a catholic church) is?

Taxonomy
narthex, the church, nave, exonarthex, free encyclopedia, Floorplan, porch, esonarthex, entrance, Chora Church, external structure, body, traditions, priest, faithful, liturgical east, church building, search.

Defination from the web:
narthex of a church is the entrance or lobby area, located at the end of the nave, at the far end from the church's main altar. Traditionally the narthex was a part of the church building, but was not considered part of the church proper. ... Narthex in an Eastern Orthodox temple. ...