Ruling based on popular decisions (9)

I believe the answer is:

democracy

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'ruling' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for democracy that I've seen before include "The least worst political system?" , "expression of popular will?" , "form of government" , "Government of/by/for all the people" .)

I've seen this clue in The Globe and Mail and The Guardian.

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