1.  A plant of the genus Dipsacus, of which one species (Dipsacus 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. [1913 Webster]
" Small teasel is Dipsacus pilosus, wild teasel is Dipsacus sylvestris." [1913 Webster]

2.  A bur of this plant. [1913 Webster]

3.  Any contrivance intended as a substitute for teasels in dressing cloth. [1913 Webster]

   To subject, as woolen cloth, to the action of teasels, or any substitute for them which has an effect to raise a nap. [1913 Webster]

teasel, n. & v. (also teazel, teazle)
--n.
1 any plant of the genus Dipsacus, with large prickly heads that are dried and used to raise the nap on woven cloth.
2 a device used as a substitute for teasels.
--v.tr. dress (cloth) with teasels.

Derivative:
teaseler n.

Etymology:
OE t{aelig}s(e)l, = OHG zeisala (as TEASE)

common teasel, fuller's teasel, wild teasel