Piece of furniture not what’s been swapped around (7)

I believe the answer is:

whatnot

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'piece of furniture' is the definition.
(I've seen this before)

'not what's been swapped around' is the wordplay.
'not what' can be anagrammed to 'WHATNOT'.
But, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for whatnot that I've seen before include "Bric-a-brac stand" , "Stand with shelves for small items" , "Thing whose name is temporarily forgotten" , "A stand with shelves for small objects" , "Portable ornament stand" .)

I've seen this clue in The Times.

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