Pay out a third of a rouble twice! (6)

I believe the answer is:

double

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'twice' is the definition.
(synonyms)

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

(Other definitions for double that I've seen before include "With two equal parts" , "Multiply by two" , "understudy" , "Bet - twice as much" , "with which darts player gets leg over?" .)

I've seen this clue in the Evening Standard.

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