The Collaborative International Dictionary
mail car
mail car \mail car\ n. A railway car of special design used for the transportation and sorting of mail en route to its destination, and having employees of the post office inside to perform those functions.
WordNet
mail car
n. a railway car in which mail is transported and sorted
Usage examples of "mail car".
Two passenger, cars, the stockcar for the horses, two freight cars, the mail car.
With well-rehearsed speed, they proceeded to take charge of the mail car, isolating it from the rest of the train.
He had immediately drawn the conductor's attention by the businesslike way he'd gotten into the mail car and then into the safe.