The Collaborative International Dictionary of English v.0.48:

Arcturus \Arc*tu"rus\, n. [L. Arcturus, Gr. ? bearward, equiv.
   to ?; ? bear + ? ward, guard. See Arctic.] (Anat.)
   A fixed star of the first magnitude in the constellation
   Bo["o]tes.
   [1913 Webster]

   Note: Arcturus has sometimes been incorrectly used as the
         name of the constellation, or even of Ursa Major.
         [1913 Webster]

               Canst thou guide Arcturus with his sons [Rev.
               Ver.: "the Bear with her train"].  --Job xxxviii.
                                                  32.
         [1913 Webster]

WordNet (r) 3.0 (2006):

Arcturus
    n 1: the 4th brightest star and the brightest star in the
         constellation Bootes; 36 light-years from Earth