Eminent conductor (7)
I believe the answer is:
'eminent conductor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for maestro that I've seen before include "Distinguished musician - most are (anag)" , "car" , "Eminent conductor or composer" , "Master of an art, or a great conductor of music" , "Expert musician" .)