from the GNU version of the Collaborative International Dictionary of English
- n. A European composite herb (Centaurea nigra); -- so called from the resemblance of its knobbed head to an iron ball fixed on a long handle.
from The Century Dictionary and Cyclopedia
- n. The knapweed, Centaurea nigra: so called in reference to the knobbed involucres.
Sorry, no etymologies found.