apsis
noun/ˈæpsɪs/
Etymology From Latin apsis, hapsis, from Ancient Greek ἁψίς (hapsís, “arch, vault”). See also apse.
1
Architecture A recess or projection, with a dome or vault, at the east end of a church.
- Like Henry's collegiate church […] the cathedral is a cruciform basilica of the double bay system with four square bays in the central nave, western transoms, a quadrum for the choir, an apsis, and a transept with auxiliary apses.2019, A Companion to Medieval Lübeck, page 96:
2
Astronomy, Natural sciences Either of the points in the elliptical orbit of a planet, comet, or moon where it is closest or furthest from the body it orbits; examples are perihelion, aphelion, perigee, and apogee.