Audacious imp may have concern (5-3-4)
I believe the answer is:
devil-may-care
'audacious' is the definition.
(I've seen this before)
'imp may have concern' is the wordplay.
'imp' becomes 'devil' (I've seen this before).
'have concern' becomes 'care' (I've seen this in another clue).
'devil'+'may'+'care'='DEVIL-MAY-CARE'
(Other definitions for devil-may-care that I've seen before include "Cavalier" , "Cheerful, reckless" , "Insouciant (attitude)" , "Reckless, audacious" , "Negligent" .)