Sibling found in a convent or hospital (6)

I believe the answer is:

sister

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'sibling' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for sister that I've seen before include "Close relation" , "woman in hospital" , "Nurse, nun or relation" , "twin?" , "Resist about the sibling" .)

I've seen this clue in The Hindu.

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