Source : Webster's Revised Unabridged Dictionary (1913)

Clotbur \Clot"bur`\, n. [Cf. {Clote}.]
   1. The burdock. [Prov. Engl.] --Prior.

   2. Same as {Cocklebur}.

Source : WordNet®

clotbur
     n : any of several erect biennial herbs of temperate Eurasia
         having stout taproots and producing burs [syn: {burdock}]