Showy piece of music learner turned up (4)
I believe the answer is:
loud
'showy' is the definition.
(both can mean ostentatious)
'piece of music learner turned up' is the wordplay.
'piece of music' becomes 'duo' (duo is a kind of piece of music).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'turned up' shows that the letters should be reversed in order.
'duo'+'l'='duol'
'duol' reversed gives 'LOUD'.
(Other definitions for loud that I've seen before include "like the bees in Yeats's glade?" , "This speaker is" , "booming" , "Fortissimo - gaudy" , "Tasteless; of great volume" .)