sleeper - noun

a rester who is sleeping

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

an unexpected achiever of success

one of the cross braces that support the rails on a railway track

a passenger car that has berths for sleeping

pajamas with feet; worn by children

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

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

an unexpected hit

sleeper - thesaurus

crosstie   slumberer   tie