In 1953, the Supermarine ____ aptly set a world air speed record (5)

I believe the answer is:

swift

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'in' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I don't see?

I can't explain the remainder of the clue.

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(Other definitions for swift that I've seen before include "wit?" , "Rapid - writer - bird" , "Racy" , "Quick - writer" , "Quick-moving" .)

I've seen this clue in The Times.

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