The most common and most likely answer to this crossword clue is the 9 letter word UNBRIDLED
I've seen this crossword clue in Independent
U
N
B
R
I
D
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E
D
Buddy explains!

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 UNBRIDLED mean?
UNBRIDLED verb- To remove the bridle, and other tack, from (a horse or other animal).
- To remove restraint from.
- Not fitted with a bridle.
- (by extension) Without restraint or limit.