I say, Cadillac should be parked by American high-flier (6)
I believe the answer is:
icarus
'high-flier' is the definition.
(I've seen this before)
'i say cadillac should be parked by american' is the wordplay.
'say cadillac' becomes 'crus' (I can't explain this - if you can you should give a lot more credence to this answer).
'should be parked by' indicates putting letters inside.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'crus' enclosing 'a' is 'carus'.
'i'+'carus'='ICARUS'
Can you help me to learn more?
(Other definitions for icarus that I've seen before include "High-flying son of Daedalus" , "Greek mythical youth who flew too close to the sun" , "Ill-fated flyer of myth" , "Flier with wax wings" , "Ancient Greek who flew so high his wings melted" .)