noun

• (architecture) A semicircular projection from a building, especially the rounded east end of a church that contains the altar.
• The bishop's seat or throne in ancient churches.
• A reliquary, or case in which the relics of saints were kept.
• (obsolete or dialectal) An aspen tree.
• (astronomy, obsolete) Obsolete form of apsis.; The nearest and furthest points to the centre of gravitational attraction for a body in orbit. More usually called an apsis. [(architecture) A recess or projection, with a dome or vault, at the east end of a church; an apse.]