noun. A usually semicircular or polygonal, often vaulted recess, especially the termination of the sanctuary end of a church.

noun. An apsis.

noun. . In architecture: Strictly, any recess, or the termination of a building, of semicircular plan, covered by a semicircular vault or semi-dome; hence, a similar feature of polygonal plan.

noun. In ordinary use, the termination of the choir or

noun. sanctuary of any church, particularly if it presents a superficial resemblance to an apse in the stricter sense, in that it is at least approximately semicircular in plan, and vaulted: commonly equivalent to chevet, and applied to the altar extremity of a church, even if of rectangular plan and not vaulted, and including the apse-aisles, chapels, and any other adjunct to the ritual east end of a church.

noun. . In astronomy, same as apsis.

noun. undefined

noun. 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.

noun. The bishop's seat or throne, in ancient churches.

noun. A reliquary, or case in which the relics of saints were kept.

noun. A semicircular projection from a building, especially the rounded east end of a church that contains the altar.

noun. The bishop's seat or throne in ancient churches.

noun. A reliquary, or case in which the relics of saints were kept.

noun. The nearest and furthest points to the centre of gravitational attraction for a body in orbit. More usually called an apsis.

noun. In some local dialects and in archaic usage, an aspen tree.

noun. a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar

"The term apse was first used in reference to a Roman basilica, of which it was a characteristic feature."

The Wikipedia article on Apse  

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