Bellwether is an archaic word; it used to mean lead sheep of the flock. In ye olden days, the flocks were mainly ewes, and it was typically the oldest ewe that was the Bellwether. The shepherd, used to taking an afternoon nap, would put a bell on the bellwether sheep so that he could locate the flock if they wandered away.
I like to think that it meant "bell wither" as in, "wither the bell goest, so goest the shepherd" ... but I often have flights of fancy ;-)
I've been corrected many times, and told that "wether" is the gelded male sheep -- but in fact, even online definitions disagree if the bellwether is the gelded male or simply an "it" of either gender; and searches for wether show that the word may actually be related to Old High German widar, meaning ram. In my flock, leadership has rotated between ewes and wethers so in general it would be hard to draw conclusions!
Special bonus: there is an old Nursery Rhyme that has Bellwether in it:
Bell-wether o' Barking cries baa, baa,
How many sheep have we lost to-day?
Nineteen have we lost, one have we fun*,
Run Rockie, run Rockie, Run, run, run.
And to make it even more appropriate, this is a traditional British knitting rhyme sung to track rounds and decreases as a stocking is knitted!
*'Fun' means 'found'.
And besides, at the time, fuzzystuff.com was taken ... so was bellwether.com, so I became TheBellwether.com. Because, there is only one ;-)