We don't have synonyms for syndic yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are synodic.
(n) :
a government official, a magistrate, especially one of the Chief Magistrates of Geneva
"1923: 'To-morrow, after the midday prayer, mount an ass and make for the Habb?n?yah quarter and there enquire for the house of the syndic Barakah, known as Ab? Sh?mah.' -- The Thousand Nights and One Night, tr. Powys Mathers"
(n) :
a government official, a magistrate, especially one of the Chief Magistrates of Geneva
"1923: 'To-morrow, after the midday prayer, mount an ass and make for the Habb?n?yah quarter and there enquire for the house of the syndic Barakah, known as Ab? Sh?mah.' -- The Thousand Nights and One Night, tr. Powys Mathers"