A timber sleeper? (3)
I believe the answer is:
log
This could be a double definition.
'a timber' is the first definition.
(thesaurus)
'sleeper?' is the second definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
Can you help me to learn more?
(Other definitions for log that I've seen before include "Lump of wood or ship's diary" , "Nautical record in timber?" , "Official record of events" , "Sea captain's diary of voyage" , "fuel consumed" .)