Composed part of a musical miscellany (4)
I believe the answer is:
calm
'composed' is the definition.
(similar in meaning)
'part of a musical miscellany' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'CALM' is hidden within 'musical miscellany'.
(Other definitions for calm that I've seen before include "Unruffled, not excited" , "Cool, composed" , "Placid, unexcited" , "Halcyon" , "Self-possessed" .)