Discerning piano with blue note occasionally (7)
I believe the answer is:
prudent
'discerning' is the definition.
(thesaurus)
'piano with blue note occasionally' is the wordplay.
'piano' becomes 'p'.
'with' means one lot of letters go next to another.
'blue' becomes 'rude' (I've seen this before**).
'occasionally' indicates alternate letters.
The alternating letters of 'note' are 'nt'.
'p'+'rude'+'nt'='PRUDENT'
(Other definitions for prudent that I've seen before include "Showing care and thought for the future" , "Wise and cautious" , "Acting with care for the future" , "Cautious and circumspect" , "With care/forethought" .)