synodic

Latin synodicus, Ancient Greek συνοδικός (sunodikós, “of or related to an assembly or meeting”). Equivalent to synod +‎ -ic.

• (UK) IPA^(key): /sɪˈnɒd.ɪk/
• (US) IPA^(key): /sɪˈnɑd.ɪk/

synodic (not comparable)

1. of, related to or produced by a synod; synodal
   • 1664, Edward Stillingfleet, A Rational Account of the Grounds of Protestant Religion:

     a synodical epistle

2. (astronomy) Of or pertaining to the conjunction of two or more heavenly bodies

   a synodical month

   the synodical revolution of the moon or a planet