Argument over railway concern (5)
I believe the answer is:
worry
'concern' is the definition.
('worry' can be a synonym of 'concern')
'argument over railway' is the wordplay.
'argument' becomes 'row' (I've seen this before).
'over' is a reversal indicator.
'railway' becomes 'ry' (abbreviation for railway).
'row' in reverse letter order is 'wor'.
'wor'+'ry'='WORRY'
(Other definitions for worry that I've seen before include "Bother" , "(Feel) anxiety" , "Fret, be disturbed in mind" , "'Anxiety, uneasiness (5)'" , "Concern, anxiety, uneasiness" .)