Rail-riding wanderer (4)
I believe the answer is:
hobo
'rail-riding wanderer' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for hobo that I've seen before include "Itinerant" , "Homeless American" , "Vagrant, tramp" , "Tramp (US)" , "Deer, situated at the back" .)