Ladies out not needing coats so long (5)

I believe the answer is:

adieu

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'so long' is the definition.
(both can mean goodbye)

I can't explain the rest of the clue.

(Other definitions for adieu that I've seen before include "Gallic goodbye" , "Goodbye in France" , "Adios, Arrivederci" , "the last word in Paris" , "So long abroad" .)

I've seen this clue in The Telegraph.

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