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A biennial Eurasian thistle (Cirsium vulgare) in the composite family, naturalized in North America and having heads of purplish flowers and spiny stems and leaves.
[From its large head.]
a tall, spiny thistle, Cirsium vulgare, having heads of pink to purple flowers: a common weed in North America.
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|Noun||1.||bull thistle - European thistle with rather large heads and prickly leaves; extensively naturalized as a weed in the United States|