a castrated goat or sheep. Castration is performed on sheep because it helps to improve the quality of the wool.
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The term [bellwether] derives from the Middle English bellewether and refers to the practice of placing a bell around the neck of a castrated ram (a wether) leading the flock of sheep. A shepherd could then note the movements of the flock by hearing the bell, even when the flock was not in sight.
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And he had experience of the like brood beasts and of springers, greasy hoggets and wether wool, having been some years before actuary for Mr Joseph Cuffe, a worthy salesmaster that drove his trade for live stock and meadow auctions hard by Mr Gavin Low's yard in Prussia street.