Crossword Genius

It's a possibility for a drinker (4)

Ross

I believe the answer is:

asti

I'm a little stuck... Click here to teach me more about this clue!

'a drinker' is the definition.
Both the definition and answer are singular nouns.
Perhaps they are linked in a way I don't understand?

'it's a possibility' is the wordplay.
'it's a' anagrams to 'ASTI'.
However, I am not sure how this is indicated.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for asti that I've seen before include "18" , "Piedmont wine city, SE of Turin" , "Italian white wine" , "Source of fizz" , "It's a (anag) - wine" .)

I've seen this clue in The Globe and Mail.
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