Son with uniform in sports car looking self-satisfied (4)
I believe the answer is:
smug
'self-satisfied' is the definition.
(synonyms)
'son with uniform in sports car looking' is the wordplay.
I cannot really see how this works, but
'son' could be 's' (genealogical abbreviation for son) and 's' is found within the answer.
'uniform' could be 'u' (phonetic alphabet: alpha, bravo, charlie etc.) and 'u' is found within the answer.
'car' could be 'mg' and 'mg' is found in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for smug that I've seen before include "looking pleased with itself" , "Self-righteously complacent" , "Full of oneself" , "Irritatingly self-satisfied" , "Superior" .)