Journey on such a train can have only one end (7)
I believe the answer is:
nonstop
'journey' is the definition.
(I know that nonstop is a type of flight)
'one end' is the wordplay.
'one' becomes 'non' (I can't justify this - if you can you should believe this answer much more).
'end' becomes 'stop' (stopping is a kind of ending).
'non'+'stop'='NONSTOP'
'on such a train can have only' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for nonstop that I've seen before include "Uninterrupted" , "Without halting" , "Never-ending" , "without rest" , "Round-the-clock, unceasing" .)