1seize and take legal custody of (something, especially a vehicle, goods, or documents) because of an infringement of a law:vehicles parked where they cause an obstruction will be impounded
2shut up (domestic animals) in a pound or enclosure:the cattle were rounded up and impounded
lock up (someone):almost forgotten were the poor unfortunates impounded in the prison
3(of a dam) hold back (water):it will impound a reservoir 130 miles long