We don't have synonyms for sabbatharian yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are Sabbatarian.
(n) :
Alternative spelling of Sabbatarian. [A person who regards and keeps the seventh day of the week ("Saturday", the Israelite or Jewish Sabbath) as holy in conformity with the fourth commandment of the Decalogue, such as an Orthodox Jew, Seventh-day Adventist, Seventh Day Baptist, a member of the Church of God (Seventh Day); a Sabbath-keeper, a Saturday-keeper.]
(n) :
Alternative spelling of Sabbatarian. [A person who regards and keeps the seventh day of the week ("Saturday", the Israelite or Jewish Sabbath) as holy in conformity with the fourth commandment of the Decalogue, such as an Orthodox Jew, Seventh-day Adventist, Seventh Day Baptist, a member of the Church of God (Seventh Day); a Sabbath-keeper, a Saturday-keeper.]