Colt’s enclosure, reckons Cockney? (6)

I believe the answer is:

rustle

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'colt's' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I can't explain the remainder of the clue.

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(Other definitions for rustle that I've seen before include "Steal stock" , "making little noise" , "Make sound as of paper crumpling - or steal cattle" , "Whisper softly" , "Swish - steal cattle" .)

I've seen this clue in the Sydney Morning Herald.

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