Actively moving around in Leith (5)

I believe the answer is:

lithe

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

'leith' is the wordplay.
'leith' can be anagrammed to 'LITHE'.
Though, I am not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for lithe that I've seen before include "grace" , "Supple and graceful" , "Able to move and bend gracefully" , "Slim and supple" , "Moving and bending with ease" .)

I've seen this clue in the Evening Standard.

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