A semicircular or polygonal recess projecting from a building

• Especially the rounded east end of a church housing the altar

建筑中半圆形或多边形的突出凹室

• 尤指教堂祭坛所在的东端半圆形后殿

Historical: the bishop’s ceremonial seat or throne in early churches

历史：早期教堂中主教的礼仪座位或宝座

Historical: a reliquary, a container for saints’ relics

历史：圣髑匣，用于存放圣徒遗物的容器

Obsolete: variant of apsis, an extreme point of an orbit

古称：apsis 的旧称，指轨道的极点