A leader or indicator of trends; the sheep or goat that wears a bell and leads the flock.
Compound of 'bell' plus 'wether' (a castrated ram). The lead animal wore a bell to help shepherds track the flock by sound.
The metaphorical power of bellwether proves that centuries-old pastoral language still shapes how we discuss economics and politics—we're still following the bell, just the trends instead of sheep.
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