noun, plural ap·si·des [ap-si-deez] /ˈæp sɪˌdiz/.
Origin of apsis
Examples from the Web for apsides
This secular displacement of the line of the apsides brings a sixth complication to the motion of our abiding-place.Urania|Camille Flammarion
The two are joined by a diameter called the line of the apsides.The Sailor's Word-Book|William Henry Smyth
The line of apsides of a large proportion of comets will be approximately coincident with the solar orbit.Comets and Meteors|Daniel Kirkwood
The “line of apsides” is that which joins them, forming the major axis of the orbit.
This point was called "the excentric," and the line from the excentric to the Earth was called "the line of apsides."The Science of the Stars|E. Walter Maunder