1. Any of several Old World coarse prickly-leaved shrubs and subshrubs having milky juice and yellow flowers; widely naturalized; often noxious weeds in cultivated soil
   - sow thistle 
2. Tall Old World biennial thistle with large clasping white-blotched leaves and purple flower heads; naturalized in California and South America
   - lady's thistle, Our Lady's mild thistle, holy thistle, blessed thistle, Silybum marianum

Derived forms: milk thistles

Type of: bush, herb, herbaceous plant, shrub

Part of: genus Silybum, genus Sonchus, Silybum, Sonchus

Encyclopedia: Milk thistle

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