sleeper

Concise Oxford English Dictionary © 2008 Oxford University Press:
sleeper/ˈsliːpə(r)/

▶noun

• 1 a sleeping car or a train carrying sleeping cars.

  ■ N. Amer. a sofa or chair that converts into a bed.

  ■ chiefly N. Amer. a sleepsuit for a baby or small child.

• 2 a film, book, play, etc. that eventually achieves success after initially attracting little attention.

• 3 a secret agent who remains inactive for a long period while establishing a secure position.

• 4 Brit. a ring or bar worn in a pierced ear to keep the hole from closing.

• 5 Brit. a wooden or concrete beam laid transversely under railway track to support it.

• 6 a stocky fish with mottled coloration. [Dormitator and other genera.]