We don't have synonyms for synaxis yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are syntaxis and synaxes.
(n) :
(Christianity) A day following a Great Feast in the Eastern Orthodox and Eastern Catholic churches, on which a person related to the events is remembered. For example, the Synaxis of John the Baptist follows the Theophany (Baptism of Christ), the Synaxis of the Archangel Gabriel follows the Annunciation, and the Synaxis of the Theotokos follows Christmas Day.
(n) :
(Christianity) A day following a Great Feast in the Eastern Orthodox and Eastern Catholic churches, on which a person related to the events is remembered. For example, the Synaxis of John the Baptist follows the Theophany (Baptism of Christ), the Synaxis of the Archangel Gabriel follows the Annunciation, and the Synaxis of the Theotokos follows Christmas Day.