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.
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   3. Anything to which attention is strongly turned; a center
      of attraction.
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            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"