Quick definitions from WordNet (woolly thistle)
▸ noun: thistle of western North America having white woolly leaves
▸ noun: biennial Eurasian white hairy thistle having pale purple flowers; naturalized in North America
▸ noun: thistle of western North America having white woolly leaves
▸ noun: biennial Eurasian white hairy thistle having pale purple flowers; naturalized in North America