Search Result for "bellwether": 
Wordnet 3.0

NOUN (2)

1. someone who assumes leadership of a movement or activity;

2. sheep that leads the herd often wearing a bell; 



The Collaborative International Dictionary of English v.0.48:

Bellwether \Bell"weth`er\, n.
   1. A wether, or sheep, which leads the flock, with a bell on
      his neck.
      [1913 Webster]

   2. Hence: A leader. [Contemptuous] --Swift.
      [1913 Webster]


WordNet (r) 3.0 (2006):

bellwether
    n 1: someone who assumes leadership of a movement or activity
    2: sheep that leads the herd often wearing a bell