How to disconcert a storey (5)

I believe the answer is:

floor

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'storey' is the definition.
(I know that storey can be written as floor)

I can't explain the remainder of the clue.

(Other definitions for floor that I've seen before include "Disconcert" , "Stump" , "American story" , "Knock down - planking" , "Storey of a building" .)

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

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