Execution needed to make 90% (10)

I believe the answer is:

decimation

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'execution' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?

I don't understand the rest of the clue.

Can you help me to learn more?

(Another definition for decimation that I've seen is " Significant destruction".)

I've seen this clue in The Irish Times.

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