Transport Clive arranged to accommodate ambassador's return (7)
I believe the answer is:
vehicle
'transport' is the definition.
(vehicle is a kind of transport)
'clive arranged to accommodate ambassador's return' is the wordplay.
'arranged' indicates an anagram.
'to accommodate' means one lot of letters goes inside another.
'ambassador' becomes 'he' (His or Her Excellency).
'return' shows that the letters should be reversed in order.
'he' written backwards gives 'eh'.
'clive' anagrammed gives 'vicle'.
'vicle' enclosing 'eh' is 'VEHICLE'.
(Other definitions for vehicle that I've seen before include "Channel - conveyance" , "Oil, for example" , "Means of conveyance" , "Structure for transporting" , "Means of transport" .)