Apse

1. A reliquary, or case in which the relics of saints were kept.
1. A projecting part of a building, esp. of a church, having in the plan a polygonal or semicircular termination, and, most often, projecting from the east end. In early churches the Eastern apse was occupied by seats for the bishop and clergy.
2. The bishop's seat or throne, in ancient churches.

This word is also written apsis and absis.