What is "owl train"

Owl \Owl\ (oul), n. [AS. [=u]le; akin to D. uil, OHG. [=u]wila, G. eule, Icel. ugla, Sw. ugla, Dan. ugle.]

1. (Zo["o]l.) Any species of raptorial birds of the family Strigid[ae]. They have large eyes and ears, and a conspicuous circle of feathers around each eye. They are mostly nocturnal in their habits.

   Note: Some species have erectile tufts of feathers on the head. The feathers are soft and somewhat downy. The species are numerous. See Barn owl, Burrowing owl, Eared owl, Hawk owl, Horned owl, Screech owl, Snowy owl, under Barn, Burrowing, etc.

   Note: In the Scriptures the owl is commonly associated with desolation; poets and story-tellers introduce it as a bird of ill omen. . . . The Greeks and Romans made it the emblem of wisdom, and sacred to Minerva, -- and indeed its large head and solemn eyes give it an air of wisdom.
   --Am. Cyc.

2. (Zo["o]l.) A variety of the domestic pigeon.

   Owl monkey (Zo["o]l.), any one of several species of South American nocturnal monkeys of the genus Nyctipithecus. They have very large eyes. Called also durukuli.

   Owl moth (Zo["o]l.), a very large moth ( Erebus strix). The expanse of its wings is over ten inches.

   Owl parrot (Zo["o]l.), the kakapo.

   Sea owl (Zo["o]l.), the lumpfish.

   Owl train, a cant name for certain railway trains whose run is in the nighttime.

n. (context slang English) A railway train that travels during the night.