Work for the railway (4)
I believe the answer is:
line
I believe this clue is a double definition.
'work' is the first definition.
(thesaurus)
'the railway' is the second definition.
(line is a kind of railway)
'for' acts as a link.
(Other definitions for line that I've seen before include "Some poetic feet; boundary, when drawn" , "Railway track; policy" , "job" , "cover on the inside" , "An American queue" .)