Condemn a railway after one short month (5)
I believe the answer is:
decry
'condemn' is the definition.
(synonyms)
'a railway after one short month' is the wordplay.
'a railway' becomes 'ry' (abbreviation).
'after' says to put letters next to each other.
'one short month' becomes 'dec' (abbreviation for December; 'short' indicates a short form).
'ry' put after 'dec' is 'DECRY'.
(Other definitions for decry that I've seen before include "Run down" , "Disparage, put down" , "Disapprove of" , "'Condemn, belittle (5)'" , "Speak of in slighting way, belittle" .)