Twenty, but no more in 1 (5)

I believe the answer is:

score

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'twenty' is the definition.
(synonyms)

I cannot understand how the rest of the clue works.

(Other definitions for score that I've seen before include "Keep count" , "Reckoning" , "Number of goals/points" , "Tally; group of twenty" , "Notch; twenty" .)

I've seen this clue in The Irish News.

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