Rally vehicle going west then east (4)
I believe the answer is:
race
'rally' is the definition.
(thesaurus)
'vehicle going west then east' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'going west' says the letters should be written in reverse.
'then' means one lot of letters go next to another.
'east' becomes 'e' (synonyms).
'car' in reverse letter order is 'rac'.
'rac'+'e'='RACE'
(Other definitions for race that I've seen before include "Move fast" , "put their skates on" , "Care about contest" , "Run fast" , "Run swiftly" .)