The most common and most likely answer to this crossword clue is the 6 plus 7 letter word CLAUDE DEBUSSY
C
L
A
U
D
E
D
E
B
U
S
S
Y
Buddy explains!
The straight part
We know that "French musician" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case french musician = claude debussy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.