sleeper sleeper /ˈsliːpɝ/

noun

1. () A rester who is sleeping  ( slumberer , sleeper )
   a rester who is sleeping
   
   
2. An unexpected hit  ( sleeper )
   an unexpected hit
    That movie was the sleeper of the summer
   that movie was the sleeper of the summer
   
3. Tropical fish that resembles a goby and rests quietly on the bottom in shallow water  ( sleeper , sleeper goby )
   tropical fish that resembles a goby and rests quietly on the bottom in shallow water
   
4. [ N. American] A piece of furniture that can be opened up into a bed  ( sleeper [ N. American] )
   a piece of furniture that can be opened up into a bed
    The living room's sleeper sofa is perfect for when we have overnight guests.
   The living room's sleeper sofa is perfect for when we have overnight guests.
   
   
5. [ N. American] Pajamas with feet; worn by children  ( sleeper [ N. American] )
   pajamas with feet; worn by children
   
6. A passenger car that has berths for sleeping  ( sleeper , sleeping car , wagon-lit )
   a passenger car that has berths for sleeping
   
   
7. [British] One of the cross braces that support the rails on a railway track  ( crosstie [ N. American] , railroad tie [ N. American] , sleeper [British] , tie [ N. American] )
   one of the cross braces that support the rails on a railway track
    The British call a railroad tie a sleeper
   the British call a railroad tie a sleeper
   
   
8. An unexpected achiever of success  ( sleeper )
   an unexpected achiever of success
    The winner was a true sleeper--no one expected him to get it
   the winner was a true sleeper--no one expected him to get it
   
9. A spy, saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal  ( sleeper )
   a spy, saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal