The Collaborative International Dictionary of English v.0.48:

Synodic \Syn*od"ic\, Synodical \Syn*od"ic*al\, a. [L. synodicus,
   Gr. ?: cf. F. synodique.]
   1. (Eccl.) Of or pertaining to a synod; transacted in, or
      authorized by, a synod; as, synodical proceedings or
      forms. "A synodical epistle." --Bp. Stillingfleet.
      [1913 Webster]

   2. (Astron.) Pertaining to conjunction, especially to the
      period between two successive conjunctions; extending from
      one conjunction, as of the moon or a planet with the sun,
      to the next; as, a synodical month (see Lunar month, under
      Month); the synodical revolution of the moon or a
      planet.
      [1913 Webster]