Only a single, dash it! (3)

I believe the answer is:

run

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'it' is the definition.
The definition suggests a singular noun which matches the answer.

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for run that I've seen before include "Dart" , "Chicken enclosure" , "Cricket score; go" , "Organise - series" , "Enter a race" .)

I've seen this clue in the Evening Standard.

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