a tall, spiny thistle, Cirsium vulgare, having heads of pink to purple flowers: a common weed in North America.
Origin of bull thistle
First recorded in 1860–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for bull thistle
Who picked out that old cross between a split-saw and a bull-thistle to umpire this muster?The Skipper and the Skipped|Holman Day