The most common and most likely answer to this crossword clue is the 9 letter word STORMIEST
I've seen this crossword clue in Independent
S
T
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R
M
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More clues leading to the result STORMIEST
Buddy explains!

The straight part
We know that "(9)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case (9) = stormiest.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 STORMIEST mean?
STORMIEST adjective- Of or pertaining to storms.
- Characterized by, or proceeding from, a storm; subject to storms; agitated with strong winds and heavy rain.
- Proceeding from violent agitation or fury.
- Violent; passionate; rough.