Crossword Genius

In communications code, the `iF^i word (7)

Ross

I believe the answer is:

foxtrot

I'm a little stuck... Click here to teach me more about this clue!

'in' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

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

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