Once more, a drink around midday (5)

I believe the answer is:

again

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'once more' is the definition.
('again' can be a synonym of 'once more')

'a drink around midday' is the wordplay.
'a drink' becomes 'jar' (colloquial).
'around' indicates the central letters.
'midday' becomes 'gain' (I can't justify this - if you can you should give a lot more credence to this answer).
The middle letter of 'jar' is 'a'.
'a'+'gain'='AGAIN'

Can you help me to learn more?

(Other definitions for again that I've seen before include "One more time, encore" , "Here we go ___" , "Ocne more" , "'Another time, once more (5)'" , "Repeatedly" .)

I've seen this clue in the Evening Standard.

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