Horrific travel on railway (4)
I believe the answer is:
gory
'horrific' is the definition.
(thesaurus)
'travel on railway' is the wordplay.
'travel' becomes 'go' ('go' can be a synonym of 'travel').
'on' is a charade indicator (letters next to each other).
'railway' becomes 'ry' (abbreviation for railway**).
'go'+'ry'='GORY'
(Other definitions for gory that I've seen before include "Covered in blood" , "Violent; bloody" , "Horrific" , "Involving much bloodshed" , "Bloodstained" .)