Train travel (4)
I believe the answer is:
rail
'train travel' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rail that I've seen before include "Protest strongly (at)" , "Water bird; bar" , "Supported bar - inveigh" , "Means of transport" , "20 backwards, that 7 runs on" .)