Open English Wordnet
Nouns
(n)sleepera spy or saboteur or terrorist planted in an enemy country who lives there as a law-abiding citizen until activated by a prearranged signal (n)sleeperan unexpected achiever of success“the winner was a true sleeper--no one expected him to get it” (n)sleeperpajamas with feet; worn by children (n)sleepera piece of furniture that can be opened up into a bed (n)sleeper, sleeper gobytropical fish that resembles a goby and rests quietly on the bottom in shallow water (n)sleeperan unexpected hit“that movie was the sleeper of the summer” 