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.
      [1913 Webster]

   Note: In the United States, each State sends two senators for
         a term of six years to the national Congress.
         [1913 Webster]

   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

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "senator":
   MP, Member of Congress, Member of Parliament, alderman,
   assemblyman, chosen freeholder, city father, congressman,
   congresswoman, councilman, floor leader, lawgiver, lawmaker,
   legislator, majority leader, minority leader, party whip,
   representative, solon, state senator, whip



Bouvier's Law Dictionary, Revised 6th Ed (1856):

SENATOR, government. One who is a member of a senate.
     2. No person shall be a senator [of the national senate] who shall not
have attained the age of thirty years, and been nine years a citizen of the
United States and who shall not when elected, be an inhabitant of that state
for which he shall be chosen. Const. U. S. art. 1, s. 3, cl. 5. Vide 1 Kent,
Com. 224 Story on the Const. 726 to 730.