in astronomy, a term used indifferently for either of the two points of a planet's orbit, where it is at the greatest or least distance from the sun or earth. Hence the line connecting these points is called the line of the apsidæ. See Astronomy.

Apsis, among ecclesiastical writers, denotes the inner part of the ancient churches, answering to the modern choir. It is also used for the bishop's throne, and sometimes for the ambo. See Ambo.