one who observes Saturday as the Sabbath (as in Judaism)
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.
pertaining to the Sabbath and its observance
Of or pertaining to the Sabbath, or the tenets of Sabbatarians.