Trains kept one kilometre away from this part of the church (8)
I believe the answer is:
transept
'this part of the church' is the definition.
('transept' is part of 'church')
'trains kept one kilometre away from' is the wordplay.
I cannot quite understand how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is located in the answer.
'from' could be 'e' (I've seen this in other clues) and 'e' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for transept that I've seen before include "It crosses the nave in church" , "Crossing part of a church" , "Patterns found in parts of church" , "Side part of a church" , "Part of church off aisle" .)