Wagon-lit (7)
I believe the answer is:
sleeper
'wagon-lit' is the definition.
(synonyms)
This is all the clue.
(Other definitions for sleeper that I've seen before include "Spy; part of railway" , "An overnight train?" , "Earring" , "Brace to support rail on track" , "Beam across railway track or berth on ship" .)