No longer the Nag's Head (4)

I believe the answer is:

then

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'no longer' is the definition.
Both the answer and definition are adverbs. Perhaps there's a link between them I don't understand?

'the nag's head' is the wordplay.
'head' suggests taking the first letters.
The initial letter of 'nags' is 'n'.
'the'+'n'='THEN'

Can you help me to learn more?

(Other definitions for then that I've seen before include "At that time; next" , "Consequently" , "Afterwards - as a result" , "Subsequently - previously" , "soon?" .)

I've seen this clue in the Evening Standard.

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