| See under apsis. |
[ap-sis] 
[-si-deez] . | 1. | Astronomy. either of two points in an eccentric orbit, one (higher apsis) farthest from the center of attraction, the other (lower apsis) nearest to the center of attraction. |
| 2. | Architecture. an apse. |
| apsis (āp'sĭs) Pronunciation Key
Plural apsides (āp'sĭ-dēz') In the path of an orbiting body, either of the two points at which it is closest to or farthest away from the body it is orbiting. See also apoapsis, periapsis. |