Calm observed around queen, note (6)
I believe the answer is:
serene
'calm' is the definition.
(synonyms)
'observed around queen note' is the wordplay.
'observed' becomes 'seen' (synonyms).
'around' means one lot of letters goes inside another.
'queen' becomes 'r' (r is abbreviation regina. e.g. in ER ).
'note' becomes 'e' (musical note).
'seen' going around 'r' is 'seren'.
'seren'+'e'='SERENE'
(Other definitions for serene that I've seen before include "Not agitated" , "Peaceful and calm in manner" , "still" , "Peaceful and unruffled" , "Calm, untroubled" .)