Apse (noun)

A semicircular or polygonal recess in a church or other building, typically at the eastern end and often containing the altar.

Origin:

Late middle english: from latin apsis, from greek hapsis "arch, vault".

Examples:

1. The apse of the cathedral was decorated with frescoes.
2. The altar was located in the apse of the church.
3. The apse was illuminated by a large rose window.
4. The apse was added to the church in the 12th century.
5. The choir was situated in the apse of the cathedral.