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Don't invest in dodgy pocketknives with Russian money (6)

Ross

I believe the answer is:

kopeck

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'don't' is the definition.
Both the answer and definition are singular nouns.
Perhaps there's a link between them I don't understand?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for kopeck that I've seen before include "little Russian money" , "Russian coin" , "One hundred of these make one rouble" , "One-hundredth of a rouble" , "Russian copper" .)

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