Adjective
Of or pertaining to a synod; transacted in, or authorized by, a synod; as, synodical proceedings or forms.
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.
Source: Webster's dictionary