The most common and most likely answer to this crossword clue is the 6 letter word COTTAS
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The straight part
We know that "Ecclesiastical garb" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ecclesiastical garb = cottas.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 COTTAS mean?
COTTAS noun- A surplice, in England and America usually one shorter and less full than the ordinary surplice and with short sleeves, or sometimes none.
- A kind of coarse woollen blanket.