'Hwyl fawr', as they say in the Valleys (11)
I believe the answer is:
valediction
'hwyl fawr' is the definition.
('goodbye' in Welsh - a valediction is a farewell)
I can't explain the rest of the clue.
(Another definition for valediction that I've seen is " Farewell".)
I've seen this clue in The Guardian.
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