The most common and most likely answer to this crossword clue is the 9 letter word FASCINATE
I've seen this crossword clue in The Daily Telegraph
F
A
S
C
I
N
A
T
E
Buddy explains!

The straight part
We know that "Charm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case charm = fascinate.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.
What does FASCINATE mean?
FASCINATE verb- To evoke an intense interest or attraction in someone.
- To make someone hold motionless; to spellbind.
- To be irresistibly charming or attractive to.