Playing flute penning a French musical (7)
I believe the answer is:
tuneful
'musical' is the definition.
(I've seen this before)
'playing flute penning a french' is the wordplay.
'playing' is an anagram indicator.
'penning' is an insertion indicator.
'a french' becomes 'un' ('a' in French).
'flute' with letters rearranged gives 'teful'.
'teful' enclosing 'un' is 'TUNEFUL'.
(Other definitions for tuneful that I've seen before include "With a pleasing musical sound" , "Euphonic" , "Harmonious" , "Melodic" , "Melodious" .)