Turn to leave in vehicle (4)
I believe the answer is:
trap
'vehicle' is the definition.
(trap is a kind of vehicle)
'turn to leave' is the wordplay.
'turn' is a reversal indicator.
'to leave' becomes 'part' (parting is a kind of leaving).
'part' reversed gives 'TRAP'.
'in' is the link.
(Other definitions for trap that I've seen before include "two-wheeler" , "corner" , "Part of a snare" , "one would be ill advised to enter?" , "that may catch a speeding motorist" .)