Order the Scots find prickly? (7)

I believe the answer is:

thistle

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

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for thistle that I've seen before include "Scottish plant emblem" , "The Scottish weed?" , "Scottish national emblem" , "Scots national emblem" , "Flower of Scotland" .)

I've seen this clue in The Times.

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