A western railway is misaligned (4)
I believe the answer is:
awry
'misaligned' is the definition.
(awry can mean misaligned or wonky)
'a western railway' is the wordplay.
'western' becomes 'w'.
'railway' becomes 'ry' (abbreviation for railway).
'a'+'w'+'ry'='AWRY'
'is' acts as a link.
(Other definitions for awry that I've seen before include "oblique" , "Distorted, crooked" , "Wrong -- twisted to one side" , "Skewwhiff" , "Uneven, crooked" .)