The American Heritage® Dictionary of the English Language, 4th Edition
n. One that serves as a leader or as a leading indicator of future trends: "The degree to which the paper is censored is a political bellwether” ( Justine De Lacy).
n. The leading sheep of a flock, having a bell hung round its neck.
n. Anything that indicates future trends.
n. A stock or bond that is widely believed to be an indicator of the overall market's condition.
the GNU version of the Collaborative International Dictionary of English
n. A wether, or sheep, which leads the flock, with a bell on his neck.
n. Hence: A leader.
The Century Dictionary and Cyclopedia
n. A wether or sheep which leads the flock, usually carrying a bell on its neck.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. sheep that leads the herd often wearing a bell
n. someone who assumes leadership of a movement or activity
Word Usage
"In their books second chapter, What We Can Learn About Service from Scandinavia, Albrecht and Zemke turned to Sweden, which they referred to as a bellwether country because of a business approach developed there called service management."