1. a wether or other male sheep that leads the flock, usually bearing a bell.
2. a person or thing that assumes the leadership or forefront, as of a profession or industry.
3. a person or thing that shows the existence or direction of a trend; index.
4. a person who leads a mob, mutiny, conspiracy, or the like; ringleader.
If you promise not to castrate me
I'll be your faithful bellwether
I'll let you tie nosegays in my hair
And we'll foment ignominies together