A male goat, especially one used for breeding. Can also refer to a policeman's club or baton in some dialects.
From the name Billy, a diminutive of William, applied to male goats by the 1800s, similar to how 'jack' was used for male donkeys. The 'police club' meaning comes from the use of the name Billy for any stick or club-like object.
It's delightfully peculiar how the friendly nickname 'Billy' became attached to male goats, following a pattern where human names were given to farm animals - like 'Jack' for donkeys and 'Tom' for male cats. This linguistic habit reveals our tendency to personify animals, making them feel more like family members than livestock.
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