In formal communications, the 'F' word (7)

I believe the answer is:

foxtrot

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'in' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.

I cannot understand how the rest of the clue works.

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(Other definitions for foxtrot that I've seen before include "Lively ballroom dance" , "Ballroom dance in quadruple time" .)

I've seen this clue in the Evening Standard.

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