The Collaborative International Dictionary of English v.0.48:

Senator \Sen"a*tor\, n. [OE. senatour, OF. senatour, F.
   s['e]nateur, fr. L. senator.]
   1. A member of a senate.
      [1913 Webster]

            The duke and senators of Venice greet you. --Shak.
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   Note: In the United States, each State sends two senators for
         a term of six years to the national Congress.
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   2. (O.Eng.Law) A member of the king's council; a king's
      councilor. --Burrill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

senator
    n 1: a member of a senate