The most common and most likely answer to this crossword clue is the 5 plus 3 letter word WHITE TIE
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Buddy explains!
The straight part
We know that "(clothing) that’s brought out on formal occasions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case (clothing) that’s brought out on formal occasions = white tie.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 WHITE TIE mean?
WHITE TIE adjective- Of an event: very formal; usually requiring a tailcoat for men.