Justify one's desire to get hold of an expensive car (7)
I believe the answer is:
warrant
'justify one's' is the definition.
'warrant' can be an answer for 'justify' (synonyms). I am not certain of the 'one's' bit.
'desire to get hold of an expensive car' is the wordplay.
'desire' becomes 'want' (want is a kind of desire).
'to get hold of' indicates putting letters inside.
'an' becomes 'a'.
'expensive car' becomes 'rr' (abbreviation for Rolls Royce).
'a'+'rr'='arr'
'want' enclosing 'arr' is 'WARRANT'.
Can you help me to learn more?
(Other definitions for warrant that I've seen before include "Call for" , "Guaranty - authorisation to make an arrest" , "Permit for arrest, search of premises, etc" , "Merit, justify" , "Writ for arrest" .)