In official 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 don't see how one could define the other.

I cannot understand how the remainder of the clue works.

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

I've seen this clue in the Evening Standard.

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