sleeper Definition

1. Someone who sleeps, especially in a specified way.

Example: a light sleeper
Example: a heavy sleeper
2. Any of the horizontal wooden or concrete beams supporting the rails on a railway track.
3a. A railway carriage providing sleeping accommodation for passengers;
3b. A train with such carriages.

Example: took the sleeper to London
4. colloq
A record, film, book, etc, which suddenly becomes popular after an initial period of uninterest.
5. A spy who spends a long time establishing him- or herself as an inoffensive citizen, usually in a foreign country, preparing for the time he or she will be required to pass on information.