Start second car (9)
I believe the answer is:
hatchback
'car' is the definition.
(hatchback is a kind of car)
'start second' is the wordplay.
'start' becomes 'hatch' (I am not sure about this - if you are sure you should believe this answer much more).
'second' becomes 'back' (to second a motion is to back it).
'hatch'+'back'='HATCHBACK'
Can you help me to learn more?
(Other definitions for hatchback that I've seen before include "Style of '5-door' car" , "Car with sloping rear boot" , "Type of car with sloping rear car door" , "transport" , "Vehicle" .)