Abandon by the roadside (5)
I believe the answer is:
ditch
'abandon' is the definition.
(ditching is a kind of abandoning)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for ditch that I've seen before include "Abandon - trench" , "Get rid of; dug channel" , "give up" , "Moat" , "Narrow channel" .)