Nonsense! The vehicle backed when the other appeared! (7)
I believe the answer is:
tractor
'the other appeared' is the definition.
I can't tell whether this defines the answer.
'nonsense the vehicle backed' is the wordplay.
'nonsense' becomes 'rot' (I've seen this before).
'the vehicle' becomes 'cart' (cart is a kind of vehicle).
'backed' says the letters should be written in reverse.
'rot'+'cart'='rotcart'
'rotcart' in reverse letter order is 'TRACTOR'.
'when' acts as a link.
Can you help me to learn more?
(Other definitions for tractor that I've seen before include "I can draw" , "Farm machine used for pulling" , "Tower" , "Vehicle for pulling farm machinery" , "Vehicle used on farms" .)