The plural of apsis; multiple semicircular recesses in buildings, or in astronomy, the two points where an orbit is closest to and farthest from a celestial body.
Latin plural of 'apsis' (Greek 'hapsis'). In medieval astronomy, the term was adopted to describe orbital extremes, a meaning that persists in modern physics and astronomy.
It's wild that the same word describes both a medieval church's rounded alcove AND the points where planets swing closest and farthest from the sun—medieval scholars literally borrowed architecture terminology to explain the cosmos!
Complete word intelligence in one call. Free tier — 50 lookups/day.