What is the meaning of Sleeper?

Someone who sleeps.

That which lies dormant, as a law.

A spy, saboteur, or terrorist who lives unobtrusively in a community until activated by a prearranged signal; may be part of a sleeper cell.

A small starter earring, worn to prevent a piercing from closing.

A railway sleeping car.

A sleeper hold.

Something that achieves unexpected success after an interval of time.

Any of family Odontobutidae of goby-like bottom-feeding freshwater fish.

A nurse shark (family Ginglymostomatidae).

A type of pajama for a person, especially a child, that covers the whole body, including the feet.

An automobile which has been internally modified to excess, while retaining a mostly stock appearance in order to fool opponents in a drag race, or to avoid the attention of the police.

A sedative.

A bet placed on the gambling table and then forgotten about by the gambler.

A pod or similar device containing a person in cryosleep.

To mark a calf by cutting its ear.

A railroad tie.

A structural beam in a floor running perpendicular to both the joists beneath and floorboards above.

A heavy floor timber in a ship's bottom.

The lowest, or bottom, tier of casks.

Source: wiktionary.org