Piccolo piece with a cornet arrangement usually hard to play (8)
I believe the answer is:
concerto
'usually hard to play' is the definition.
I can't tell whether this definition defines the answer.
'piccolo piece with a cornet arrangement' is the wordplay.
'piccolo piece' becomes 'co' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' means one lot of letters goes inside another.
'arrangement' indicates an anagram.
'cornet' anagrammed gives 'oncert'.
'co' enclosing 'oncert' is 'CONCERTO'.
Can you help me to learn more?
(Other definitions for concerto that I've seen before include "Orchestral piece" , "Piece for soloist and orchestra" , "Orchestral composition" , "Musical work" , "Work for orchestra and soloist(s)" .)