The most common and most likely answer to this crossword clue is the 9 letter word UNIFORMED
I've seen this crossword clue in Independent
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More clues leading to the result UNIFORMED
Buddy explains!

The straight part
We know that "Wearing special clothes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wearing special clothes = uniformed.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 UNIFORMED mean?
UNIFORMED verb- To clothe in a uniform.
- Dressed in a uniform.
- In an occupation that requires a uniform, such as the police force or military.