[n] an unexpected hit; "that movie was the sleeper of the summer"
[n] tropical fish that resembles a goby and rests quietly on the bottom in shallow water
[n] a piece of furniture that can be opened up into a bed
[n] a passenger car that has berths for sleeping
[n] one of the cross braces that support the rails on a railway track; "the British call a railroad tie a sleeper"
[n] a rester who is sleeping
[n] an unexpected achiever of success; "the winner was a true sleeper--no one expected him to get it"
[n] a spy or saboteur planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal