Hairdo that goes well with the tea-gown? (3)

I believe the answer is:

bun

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'hairdo' is the definition.
(I know that bun is a hairdo)

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

(Other definitions for bun that I've seen before include "Small rounded bread or cake" , "Small cake or bread roll" , "Tied hair" , "Small cake - tied-up hair" , "Kind of small round cake" .)

I've seen this clue in the Evening Standard.

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