A moving spirit (6)

I believe the answer is:

petrol

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'a moving spirit' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

This is the entire clue.

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(Other definitions for petrol that I've seen before include "Common car fuel" , "Fuel for the internal combustion engine" , "Common motor fuel" , "Fuel for road vehicles" , "The juice" .)

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

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