Crossword Genius

Are they made of brushwood? (6)

Ross

I believe the answer is:

besoms

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'are they' is the definition.
The definition suggests a plural noun which matches the answer.

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Another definition for besoms that I've seen is " Brooms made of twigs".)

I've seen this clue in The Irish News.
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