We don't have synonyms for sethian yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are setian.
(n) :
A member of an ancient Christian Gnostic sect who venerated the Biblical Seth, third son of Adam and Eve, depicted in their creation myths as a divine incarnation.
(n) :
A member of an ancient Christian Gnostic sect who venerated the Biblical Seth, third son of Adam and Eve, depicted in their creation myths as a divine incarnation.