A still wine? (4)

I believe the answer is:

asti

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'wine?' is the definition.
(Italian wine)

'a still' is the wordplay.
'still' becomes 'sti' (I can't justify this - if you can you should believe this answer much more).
'a'+'sti'='ASTI'

Can you help me to learn more?

(Other definitions for asti that I've seen before include "Italian wine - (then change a letter for ...)" , "Italian white wine" , "Alcohol" , "Piedmontese white wine" , "Italian drunk" .)

I've seen this clue in the Evening Standard.

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