Ambulatory - The walkway surrounding the apse or choir section.

Ambry - The repository for consecrated oils. Also called an olearium. In the Cathedral Basilica of Saint Louis, the ambry is located near the baptismal font in the east transept.

Apse - The section of the cathedral that usually contains the altar. It is often shaped like a semicircle and traditionally faces east. (The apse of the Cathedral Basilica of St. Louis faces north.)

Baldacchino or baldachin - There are numerous spelling for this word, but they all mean the same thing - a canopy covering the altar.

Capital - The top of a column.

Cathedra - Literally a chair and the source of word "cathedral." This chair is located in the sanctuary and is used exclusively by the Archbishop.

Fascia - A flat surface that covers the ends of beams or other supporting structures.

Lunette - Half-moon shaped sections frequently seen at the base of vaulted roofs.

Narthex - The vestibule or lobby.

Nave - The main section of a cathedral or church, facing the altar.

Ombrellino - An umbrella-like device embroidered with mottos and crests. Its presence along with the tintinnabulum, in signifies the basilica status of the Cathedral Basilica.

Pendentive - A triangular structure that support a dome. In the Cathedral Basilica of Saint Louis, the pendentives of the Central Dome feature huge spread-winged angels.

Portal - Main door. The Cathedral Basilica of St. Louis is typical of most in that is has three main front portals, symbolizing the Holy Trinity.

Soffit - The underside of an arch or balcony.

Tessera - A thin slab of glass or tile which is shaped into pieces that make up a mosaic.

Most often used in its plural, which is tesserae.

Tintinnabulum - Ceremonial bell which is symbolic of a basilica. See ombrellino.

Triptych - A piece of art consisting of three panels, usually a larger central panel with two smaller side panels. Often seen in altarpieces, the triptychs of the Cathedral Basilica grace the walls of the All Saints Chapel and Our Lady's Chapel.

Transept - If the nave and apse constitute the long beam of a cross, the transepts make up the cross bar. These are large "bays" that extend from either side of the nave. In the Cathedral Basilica of Saint Louis, they feature large mosaic-covered half domes.