The Collaborative International Dictionary of English v.0.48:

Fuller \Full"er\, n. [AS. fullere, fr. L. fullo. See Full, v.
   t.]
   One whose occupation is to full cloth.
   [1913 Webster]

   Fuller's earth, a variety of clay, used in scouring and
      cleansing cloth, to imbibe grease.

   Fuller's herb (Bot.), the soapwort (Saponaria
      officinalis), formerly used to remove stains from cloth.


   Fuller's thistle or Fuller's weed (Bot.), the teasel
      (Dipsacus fullonum) whose burs are used by fullers in
      dressing cloth. See Teasel.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Teasel \Tea"sel\, n. [OE. tesel, AS. t[=ae]sel, t[=ae]sl, the
   fuller's herb. See Tease.] [Written also tassel, tazel,
   teasle, teazel, and teazle.]
   1. (Bot.) 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]

   Note: 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]

   Teasel frame, a frame or set of iron bars in which teasel
      heads are fixed for raising the nap on woolen cloth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Dipsacus fullonum
    n 1: teasel with lilac flowers native to Old World but
         naturalized in North America; dried flower heads used to
         raise a nap on woolen cloth [syn: common teasel,
         Dipsacus fullonum]