The most common and most likely answer to this crossword clue is the 9 letter word SHERWANIS
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Buddy explains!

The straight part
We know that "long coats" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case long coats = sherwanis.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 SHERWANIS mean?
SHERWANIS noun- A knee-length coat that buttons to the neck, worn by man, over a shalwar kameez, in parts of India and Pakistan.