sleeper

1. Someone who sleeps.

   I'm a light sleeper: I get woken up by the smallest of sounds.

2. That which lies dormant, as a law.
3. A spy, saboteur, or terrorist who lives unobtrusively in a community until activated by a prearranged signal; may be part of a sleeper cell.
4. A small starter earring, worn to prevent a piercing from closing.
5. A railway sleeping car.

   We spent a night on an uncomfortable sleeper between Athens and Vienna.

6. A sleeper hold.
7. Something that achieves unexpected success after an interval of time.

   A box-office bomb when it first came out, the film was a sleeper, becoming much more popular decades after being released.

8. A goby-like bottom-feeding freshwater fish of the family Odontobutidae.
9. A nurse shark (family Ginglymostomatidae).
10. A type of pajama for a person, especially a child, that covers the whole body, including the feet.

    Aaron, Devin, and Laura looked so comfy in their sleepers.

11. 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.
12. A sedative.

verb

To mark a calf by cutting its ear.

1. A railroad tie.
2. A structural beam in a floor running perpendicular to both the joists beneath and floorboards above.
3. A heavy floor timber in a ship's bottom.
4. The lowest, or bottom, tier of casks.