any of several herbs of the genus Dipsacus native to the Old World having flower heads surrounded by spiny bracts
source: WordNet 3.0
A plant of the genus Dipsacus, of which one species (D. fullonum) bears a large flower head covered with stiff, prickly, hooked bracts. This flower head, when dried, is used for raising a nap on woolen cloth.
source: Webster 1913
To subject, as woolen cloth, to the action of teasels, or any substitute for them which has an effect to raise a nap.