sleeper

sleeper (http://definr.com/sleeper)

     n 1: a rester who is sleeping [syn: slumberer]
     2: a spy planted in advance for future use but not presently
        active
     3: an unexpected achiever of success
     4: one of the cross braces that support the rails on a railway
        track; "the British call a railroad tie a sleeper" [syn: tie,
         railroad tie, crosstie]
     5: a passenger car that has berths for sleeping [syn: {sleeping
        car}, wagon-lit]
     6: tropical fish that resembles a goby and rests quietly on the
        bottom in shallow water [syn: sleeper goby]