Composed a piece of classical music (4)
I believe the answer is:
calm
'composed' is the definition.
(I've seen this before)
'a piece of classical music' is the wordplay.
'a piece of' indicates the answer is hidden within the clue.
'CALM' is hidden within 'classical music'.
(Other definitions for calm that I've seen before include "Composure or serenity" , "Unruffled, not excited" , "Tranquil, undisturbed" , "Controlled, not agitated" , "Placid and unruffled" .)