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.

A person who regards and keeps the first day of the week as holy and often considers it as a replacement for the seventh-day Sabbath, a Sunday-keeper.

A person who favors the strict observance of the Sabbath (either the sixth, seventh, or first day of the week).

A member of a non-Jewish religious sect originating in Russia distinguished by observance of Jewish rites and festivals including Saturday as the day of rest.

Of or pertaining to the Sabbath, or the tenets of Sabbatarians.