apsis
/ˈæpsɪs/noun
(pl. apsides /æpˈsaɪdiːz/)
- either of two points on the orbit of a planet or satellite that are nearest to or furthest from the body round which it moves拱（极）点。
派生词
apsidal
adjective词源
early 17th cent. (denoting the orbit of a planet)： via Latin from Greek apsis, hapsis 'arch， vault'， perhaps from haptein 'fasten， join'.