Longman Dictionary of Contemporary English
mail train
noun
EXAMPLES FROM CORPUS
▪ As the mail train thundered past and disappeared into the distance he heard the familiar sound of footsteps.
▪ Had some one been killed by the mail train?
The Collaborative International Dictionary
mail train
mail train \mail train\ n. A railroad train that carries mail.
Wiktionary
mail train
n. (context rail transport English) A train used by the postal service to transport mail, and in some cases, to sort mail en route.
WordNet
mail train
n. a train that carries mail
Usage examples of "mail train".
The bank robbery had taken place the night before last, time enough since then for him to come down by road or on the mail train.
He did not like to ask, as tempers in the upper hierarchy were notoriously short since the mail train robbery, which had been a spectacular success for the criminals.
He went into the bathroom, sat on the ring, and a huge diarrhea movement rushed out of him like a mail train highballing through a deserted station.