Narthex (narthex)

The covered vestibule of a church.
The narthex gives access to the nef (nave) and is located at the outmost westside of the church.
The grey part in the plan (Wikipedia) is the narthex.
 In the picture the narthex of the Saint-Vincent in Mâcon.
See also avant-nef and gallilée (synonyms).

Narthex - Wikipedia

Saint-Vincent - Mâcon

Nef (nave)

The longest part of a church, located between façade (facade) and abside (apse) (or the transept if there is one).
A church can have one single nave or a central nave with two or more bas-côtés (aisles, they are also part of the nave).
The axis of the nave coincides with the east-west axis of the church.
In plan the nave is indicated in pink.
The picture shows the nave and the two aisles of the Saint-Martin in Chapaize.
See also vaisseau (synonym).

Nef - Wikipedia

Saint-Martin - Chapaize

Nervure (arch rib ©)

The translation in the title is followed by this sign ©; this means that it has been "invented" by me.

A striking rib with a semicircular profile lining an arc (arch).
In the picture the nervure on the edge of an arch in a chapelle latérale (lateral chapel) of the Notre-Dame-de-la-Nativité in Bissy-sur-Fley.

Notre-Dame-de-la-Nativité - Bissy-sur-Fley

Nimbe (nimbus, halo)

An aureole surrounding the face of a saint.
The picture shows a saint with halo on a fresque (fresco) in the Notre-Dame-de-l'Assomption in Gourdon.

Notre-Dame-de-l'Assomption - Gourdon