Railway carriage (5)
'railway carriage' is the definition.
(I know that sleeper is a type of railway carriage)
This is all the clue.
(Other definitions for sleeper that I've seen before include "found on the railway" , "night train" , "Spy; part of railway" , "Railway track support" , "Beam across railway track or berth on ship" .)
(Other definitions for coach that I've seen before include "Train - or part of one!" , "Railway carriage or sports instructor" , "Teacher of sporting activity" , "Trainer - vehicle" , "Vehicle; instructor" .)