Service vehicle returned at eleven (4)
I believe the answer is:
taxi
'service vehicle' is the definition.
'taxi' can be an answer for 'vehicle' (taxi is a kind of vehicle). I'm not sure about the 'service' bit.
'returned at eleven' is the wordplay.
'returned' shows that the letters should be reversed in order.
'eleven' becomes 'xi' (Roman numerals).
'at' backwards is 'ta'.
'ta'+'xi'='TAXI'
Can you help me to learn more?
(Other definitions for taxi that I've seen before include "Transport for hire" , "run along the ground" , "Vehicle with a meter" , "Motor-cab" , "Cab for hire" .)