Vegetable vehicle? Rubbish! (6)
I believe the answer is:
carrot
'vegetable' is the definition.
(carrot is a kind of vegetable)
'vehicle? rubbish' is the wordplay.
'vehicle?' becomes 'car' (car is a kind of vehicle).
'rubbish' becomes 'rot' (both can mean nonsense).
'car'+'rot'='CARROT'
(Other definitions for carrot that I've seen before include "Pointed vegetable" , "The vegetable to induce" , "The vegetable for persuasion" , "Obstacle in race" , "Red vegetable used as inducement" .)