Mama who sang clubs wearing fine, long robe (7)

I believe the answer is:

cassock

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'robe' is the definition.
(cassock is a kind of robe)

I don't understand the rest of the clue.

(Other definitions for cassock that I've seen before include "Vestment" , "Cossack (anag.)" , "Ankle-length garment worn by priests and choristers" , "Is it a habit of the clergy" , "Long garment worn by priests" .)

I've seen this clue in The Times.

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