- a semicircular or polygonal projection of a building, esp. one at the east end of a church, with a domed or vaulted roof
- apsis (sense )
Origin of apseClassical Latin apsis, apsis
- Architecture A usually semicircular or polygonal, often vaulted recess, especially the termination of the sanctuary end of a church.
- Astronomy An apsis.
Origin of apseVariant of apsis.
plan of the 4th-century ad
St. Peter's Basilica, Rome, Italy