The most common and most likely answer to this crossword clue is the 8 letter word SCAPULAR
I've seen this crossword clue in Independent
S
C
A
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Buddy explains!
The straight part
We know that "what sister sometimes wears" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what sister sometimes wears = scapular.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 SCAPULAR mean?
SCAPULAR noun- A short cloak worn around the shoulders, adopted as part of the uniform of various religious orders, later often with an embroidered image of a saint.
- One of a special group of feathers which arise from each of the scapular regions and lie along the sides of the back.
- A bandage passing over the shoulder to support it, or to retain another bandage in place.
- A devotional object, typically consisting of two rectangular pieces of cloth (often with an embroidered image or text) joined with cloth bands and worn with one piece over the chest and one in the back.
- Of or pertaining to the scapula.