The Collaborative International Dictionary of English v.0.48:

Sabbatarian \Sab`ba*ta"ri*an\, n. [L. Sabbatarius: cf. F.
   sabbataire. See Sabbath.]
   1. One who regards and keeps the seventh day of the week as
      holy, agreeably to the letter of the fourth commandment in
      the Decalogue.
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   Note: There were Christians in the early church who held this
         opinion, and certain Christians, esp. the Seventh-day
         Baptists, hold it now.
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   2. A strict observer of the Sabbath.
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The Collaborative International Dictionary of English v.0.48:

Seventh \Sev"enth\, a. [From Seven: cf. AS. seofo[eth]a.]
   1. Next in order after the sixth;; coming after six others.
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            On the seventh day, God ended his work which he had
            made; and he rested on the seventh day from all his
            work which he had made.               --Gen. ii. 2.
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   2. Constituting or being one of seven equal parts into which
      anything is divided; as, the seventh part.
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   Seventh day, the seventh day of the week; Saturday.

   Seventh-day Baptists. See under Baptist.
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The Collaborative International Dictionary of English v.0.48:

Baptist \Bap"tist\ (b[a^]p"t[i^]st), n. [L. baptista, Gr.
   baptisth`s.]
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   1. One who administers baptism; -- specifically applied to
      John, the forerunner of Christ. --Milton.
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   2. One of a denomination of Christians who deny the validity
      of infant baptism and of sprinkling, and maintain that
      baptism should be administered to believers alone, and
      should be by immersion. See Anabaptist.
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   Note: In doctrine the Baptists of this country [the United
         States] are Calvinistic, but with much freedom and
         moderation. --Amer. Cyc.
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   Freewill Baptists, a sect of Baptists who are Arminian in
      doctrine, and practice open communion.

   Seventh-day Baptists, a sect of Baptists who keep the
      seventh day of the week, or Saturday, as the Sabbath. See
      Sabbatarian. The Dunkers and Campbellites are also
      Baptists.
      [1913 Webster] Baptistery