The word actually comes from Old Middle English, when a bell was put on the neck of a ram, also known as a wether, to lead a flock of sheep in one direction.
Firearms deliver tremendous amounts of kinetic energy at very high speeds, and wether you're an undead zombie or an immortal machete-wielding mass murderer, a shattered femur is still impossible to stand on.
Then a dozen or more were shoved off, and the Don, tall like a crane and a good natural wader, jumped in after them, seized a struggling wether, and dragged it to the opposite shore.