Inferior work accepted by railway (4)
I believe the answer is:
ropy
'inferior' is the definition.
('ropy' can be similar in meaning to 'inferior')
'work accepted by railway' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'accepted by' is an insertion indicator.
'railway' becomes 'ry' (abbreviation for railway).
'op' put inside 'ry' is 'ROPY'.
(Other definitions for ropy that I've seen before include "Slightly off-colour" , "Far from top quality" , "Slightly unwell" , "Substandard" , "Not very good" .)