The most common and most likely answer to this crossword clue is the 9 letter word CHEVALIER
I've seen this crossword clue in Financial Times
C
H
E
V
A
L
I
E
R
More clues leading to the result CHEVALIER
- Optimism about mostly sound old knight
- Gallant French actor and singer
- Sound cut in shout to encourage knight
- Sound shortened in shout to encourage Maurice?
- Knight caught her alive after struggle
- French gentleman crashing a vehicle by river
- Maurice, member of the Légion d’Honneur
- Not entirely reasonable to interrupt Joy’s gallant
- Knight who thanked heaven for little girls
- French singer, singer keeping alive, surprisingly
Buddy explains!

The straight part
We know that "Maurice/member of the Légion d’Honneur" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case maurice/member of the légion d’honneur = chevalier.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 CHEVALIER mean?
CHEVALIER noun- A cavalier; a knight.
- In tarot cards, the card between the valet and the dame