The most common and most likely answer to this crossword clue is the 9 letter word AYATOLLAH
I've seen this crossword clue in Financial Times
A
Y
A
T
O
L
L
A
H
More clues leading to the result AYATOLLAH
- Shiite leader always put on a ring, I see!
- Island repressed by domestic authority
- Religious leader’s Indian maid skirting coral reef
- Religious leader always returned greeting with thanks
- Bikini perhaps concealed by nurse as religious leader appears
- Religious leader with a ‘tally-ho!’: a maverick
- Greeting Scottish banker and a regressively religious authority
- Sort of hat a loyal religious leader appears in
- Nursemaid brings in a ring for religious leader
- Nursemaid accepts fee given by a religious leader
Buddy explains!

The straight part
We know that "Religious leader" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case religious leader = ayatollah.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 AYATOLLAH mean?
AYATOLLAH noun- A religious leader in Twelver Shi'ism.
- An authority on any subject.