Thorny subject of Blair's initial meandering discourse with his partner in crime (7-4)

I believe the answer is:

bramble-bush

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'thorny subject of blair's initial meandering discourse with his partner in crime' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

This is all the clue.

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I've seen this clue in The Independent.

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