any of several uncultivated lettuce plants, such as Lactuca serriola (or L. scariola) of Eurasia and L. canadensis (horseweed) of North America, which grow as weeds and have yellow or blue flowers, milky juice in the stem, and prickly leaves: family Asteraceae (composites)
wild lettuce in American English
any of various wild species of lettuce, having small, dandelionlike flower heads, milky juice, and, often, pricklyfoliage; esp., a lettuce (Lactuca canadensis) of E North America