Score achieved through double cross? (6)

I believe the answer is:

twenty

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'score' is the definition.
(synonyms)

I can't explain the rest of the clue.

(Other definitions for twenty that I've seen before include "Figure" , "John B Keane wrote about many young men of this age" , "with two crosses" , "Score, XX" , "No. between 5 and 1 on dartboard" .)

I've seen this clue in The Irish Times.

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