Transport will be back at eleven (4)
I believe the answer is:
taxi
'transport' is the definition.
(taxi is a kind of transport)
'will be back at eleven' is the wordplay.
'will' is a charade indicator (letters next to each other) (I've seen this in other clues).
'be back' says the letters should be written in reverse.
'eleven' becomes 'xi' (roman numeral).
'at' in reverse letter order is 'ta'.
'ta' next to 'xi' is 'TAXI'.
(Other definitions for taxi that I've seen before include "Rank occupant" , "Cab for hire" , "US currency" , "run along the ground" , "Hackney cab" .)