Crossword Genius

In which all men are brothers? (6)

Ross

I believe the answer is:

abbeys

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'brothers?' is the definition.
Although both the answer and definition are plural nouns, I can't understand how they can define each other.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for abbeys that I've seen before include "Buildings occupiedby communities of monks" , "Places of worship f" , "Religious establishments" , "Buildings occupied by communities of monks" , "Buildings occupied by monks or nuns" .)

I've seen this clue in The Globe and Mail.
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