If you want to knock off, go quietly (5)

I believe the answer is:

steal

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'go quietly' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for steal that I've seen before include "Take illegally" , "Take without permission" , "Walk off with" , "Plagiarise" , "Thieve" .)

I've seen this clue in the Evening Standard.

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