WordNet (r) 3.0 (2006):

woolly thistle
    n 1: biennial Eurasian white hairy thistle having pale purple
         flowers; naturalized in North America [syn: cotton
         thistle, woolly thistle, Scotch thistle, Onopordum
         acanthium, Onopordon acanthium]
    2: thistle of western North America having white woolly leaves
       [syn: woolly thistle, Cirsium flodmanii]