Crossword Genius

Nice mushroom a representative has left for bun (7)

Ross

I believe the answer is:

chignon

'bun' is the definition.
(thesaurus)

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

(Other definitions for chignon that I've seen before include "Topknot" , "Coil of hair at the back of the head" , "Hairstyle" , "Roll of hair worn at the nape" , "Roll of hair worn at the back of the head" .)

I've seen this clue in The Times.
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