Can you drink one twice? (6)

I believe the answer is:

double

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

I cannot understand how the remainder of the clue works.

(Other definitions for double that I've seen before include "Twin, dual" , "Multiply by two" , "Bed for two people" , "Score of forty with one dart, perhaps?" , "with which darts player gets leg over?" .)

I've seen this clue in the Evening Standard.

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