A leader or indicator of trends; originally, the sheep or goat that wears a bell and leads a flock.
Compound of 'bell' plus 'wether' (a castrated ram). The lead animal literally wore a bell so shepherds could track the entire flock.
Bellwether sheep literally had bells around their necks, and because flocks followed their lead, the word became our term for any trendsetter—from a sheep's bell came our language of influence and prediction.
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