1. [n]  one who observes Saturday as the Sabbath (as in Judaism)
2. [adj]  pertaining to the Sabbath and its observance

SABBATARIAN is a 11 letter word that starts with S.

1. \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.
   
   Note: There were Christians in the early church who held this
         opinion, and certain Christians, esp. the {Seventh-day
         Baptists}, hold it now.
   
   2. A strict observer of the Sabbath.
   
   

2. \Sab`ba*ta"ri*an\, a.
   Of or pertaining to the Sabbath, or the tenets of
   Sabbatarians.