Some classical music is serene (4)
I believe the answer is:
calm
'serene' is the definition.
(synonyms)
'some classical music is' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'CALM' is hidden in the letters of 'classical music is'.
(Other definitions for calm that I've seen before include "Peace, tranquillity" , "stained-glass window maker could need this" , "Pacific" , "Tranquil, undisturbed" , "Placid, unexcited" .)