Slack and undisciplined old airport (8)

I believe the answer is:

idlewild

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'old airport' is the definition.
I don't know anything about this answer so I cannot judge whether this works.

'slack and undisciplined' is the wordplay.
'slack' becomes 'idle' (I can't explain this - if you can you should believe this answer much more).
'and' is a charade indicator (letters next to each other).
'undisciplined' becomes 'wild' (I've seen this in another clue).
'idle'+'wild'='IDLEWILD'

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I've seen this clue in the Evening Standard.

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