A French one in a flute arrangement, is melodious (7)
I believe the answer is:
tuneful
'is melodious' is the definition.
(synonyms)
'a french one in a flute arrangement' is the wordplay.
'a french one' becomes 'un' ('one' in French).
'in' is an insertion indicator.
'arrangement' is an anagram indicator.
'flute' with letters rearranged gives 'teful'.
'un' put into 'teful' is 'TUNEFUL'.
(Other definitions for tuneful that I've seen before include "Euphonious" , "Euphonic" , "Melodious" , "With a pleasing musical sound" , "Melodic" .)