Able to steal a car (4)
I believe the answer is:
fiat
'car' is the definition.
(car manufacturer)
'able to steal a' is the wordplay.
'able' becomes 'fit' (similar in meaning).
'to steal' indicates putting letters inside.
'fit' placed around 'a' is 'FIAT'.
(Other definitions for fiat that I've seen before include "mandate" , "Decree; Italian car make" , "Command" , "Let it be done - it's a Latin order" , "Decree or official permission" .)