Crossword Genius

Using coinage, took London Underground northwards for first time (5)

Ross

I believe the answer is:

debut

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'using' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?

I cannot understand how the rest of the clue works.

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(Other definitions for debut that I've seen before include "Introduction" , "First attempt" , "First appearance, a coming-out" , "First public appearance of performer" , "Beginning, first performance" .)

I've seen this clue in The Telegraph.
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