Stiff man enters vehicle (7)
I believe the answer is:
cadaver
'stiff' is the definition.
('cadaver' can be a synonym of 'stiff')
'man enters vehicle' is the wordplay.
'man' becomes 'dave' (I've seen this before**).
'enters' indicates putting letters inside.
'vehicle' becomes 'car' (car is a kind of vehicle).
'dave' put within 'car' is 'CADAVER'.
(Other definitions for cadaver that I've seen before include "A kind of corpse" , "Stiff" , "Human corpse" , "Dead body, corpse" , "Human body dissected by medical students" .)