1. either of the two points in an elliptical orbit that are farthest from or closest to the center of attraction
Usage: astronomy
2. a semicircular or polygonal recess in a church, especially at the east end behind the altar
Usage: architecture

Examples

• The comet reaches its apsis when it is farthest from the sun.
• At apsis, the satellite’s velocity is at its minimum or maximum.
• The planet’s apsis points determine the shape of its orbital ellipse.
• The cathedral’s apsis was decorated with beautiful Byzantine mosaics.
• The choir was positioned in the apsis behind the main altar.
• Medieval churches often featured a rounded apsis at the eastern end.