Condemn a railway after one short month (5)
I believe the answer is:
decry
'condemn' is the definition.
('decry' can be a synonym of 'condemn')
'a railway after one short month' is the wordplay.
'a railway' becomes 'ry' (abbreviation for railway).
'after' says to put letters next to each other.
'one short month' becomes 'dec' (I can't justify this - if you can you should believe this answer much more).
'ry' after 'dec' is 'DECRY'.
Can you help me to learn more?
(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" .)