noun
: any of various plants of the genus Centaurea: as
a. : an annual or biennial herb ( Centaurea calcitrapa ) having a basal rosette of deeply toothed leaves, a much branched stem, and axillary or terminal heads of pinkish to purple tubular flowers surrounded by scales tipped with long stout yellow spines and being native to the Mediterranean region but widely distributed by commerce and in many places established as an aggressive weed
b. : barnaby's thistle
c. : basket flower
d. : russian knapweed