Darts player's favourite drink? (6)

I believe the answer is:

double

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'drink?' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for double that I've seen before include "Twin, dual" , "Make twice as many" , "Twice the amount" , "- - -u, (w)" , "Multiply by two" .)

I've seen this clue in the Evening Standard.

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