1. Someone who seizes and retains people or something in legal custody: Ray, Hans and the group of dog impounders drove all around the city looking for stray dogs.

The police impounders were removing vehicles that were parked illegally and causing obstructions on the street.

2. Someone who shuts domestic animals in an enclosure: Gary, the farm impounder, was moving the cattle into a special area surrounded by a fence so they could be transported to town from a mountainous area to lower fields for winter feeding.
3. A dam that holds back or confines water: The dam served as an impounder of the melting snow when the weather became warmer.