The Collaborative International Dictionary of English v.0.48:

Cynosure \Cy"no*sure\ (s?"n?-sh?r or s?n"?-sh?r; 277), n. [L.
   Cynosura theconstellation Cynosure, Gr. ????? dog's tail, the
   constellation Cynosure; ????, ????, dog + o'yra` tail.
   SeeCynic.]
   1. The constellation of the Lesser Bear (Ursa Minor), to
      which, as containing the polar star, the eyes of mariners
      and travelers were often directed.
      [1913 Webster]

   2. That which serves to direct. --Southey.
      [1913 Webster]

   3. Anything to which attention is strongly turned; a center
      of attraction.
      [1913 Webster]

            Where perhaps some beauty lies,
            The cynosure of neighboring eyes.     --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cynosure
    n 1: something that provides guidance (as Polaris guides
         mariners); "let faith be your cynosure to walk by"
    2: something that strongly attracts attention and admiration;
       "if he was the cynosure of all eyes he didn't notice"

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "cynosure":
   North Star, Polaris, acme, adductor, apotheosis, attractant,
   attrahent, beau ideal, best type, big name, celebrity, center,
   center of attraction, center of consciousness, center of interest,
   constellation, ego ideal, figure, focal point, focus,
   focus of attention, folk hero, galaxy, great man, guiding star,
   hero, heroine, ideal, idol, immortal, important person, lion,
   lodestar, luminaries, luminary, lure, magnet, man of mark,
   master spirit, mirror, name, notability, notable, paragon,
   person of note, personage, pleiad, point of convergence,
   polar star, polestar, pop hero, popular hero, popular idol,
   prime focus, public figure, shining example, social lion, somebody,
   star, superstar, worthy