sleeper

A rester who is sleeping.

One of the cross braces that support the rails on a railway track.

“the British call a railroad tie a sleeper”

Tropical fish that resembles a goby and rests quietly on the bottom in shallow water.

A passenger car that has berths for sleeping.

An unexpected achiever of success.

“the winner was a true sleeper--no one expected him to get it”

An unexpected hit.

“that movie was the sleeper of the summer”

A piece of furniture that can be opened up into a bed.

A spy or saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal.

Pajamas with feet; worn by children.