Cab returns at eleven (4)
I believe the answer is:
taxi
'cab' is the definition.
(taxi cab)
'returns at eleven' is the wordplay.
'returns' shows that the letters should be reversed in order.
'eleven' becomes 'xi' (Roman numerals).
'at' backwards is 'ta'.
'ta'+'xi'='TAXI'
(Other definitions for taxi that I've seen before include "I hail you!" , "Motor vehicle for hire with driver" , "Motor cab" , "(Of a plane) move slowly on the ground" , "Prepare to fly" .)