either of two points lying at the extremities of an eccentric orbit of a planet, satellite, etc, such as the aphelion and perihelion of a planet or the apogee and perigee of the moon. The line of apsides connects two such points and is the principal axis of the orbit
2. another name for apse (sense 1)
Derived forms
apsidal (æpˈsaɪdəl, ˈæpsɪdəl)
adjective
Word origin
C17: via Latin from Greek; see apse
apsis in American English
(ˈæpsɪs)
nounWord forms: pluralˈapsiˌdes (ˈæpsəˌdiz)
1.
that point in the elliptical orbit of the moon, a planet, etc. nearest to (lower apsis), or that farthest from (higher apsis), the gravitational focus point
2.
apse (sense 1)
Idioms:
line of apsides
Word origin
L, an arch < Gr hapsis, a fastening < haptein: see apt1