Formal wear kept nice butcher powerless (7)

I believe the answer is:

necktie

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'formal wear' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for necktie that I've seen before include "one from the old school?" , "this'll go with shirt" , "Long narrow piece of material worn knotted at the front" , "Material worn knotted round throat" , "Band in the US" .)

I've seen this clue in the Sydney Morning Herald.

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