The Collaborative International Dictionary of English v.0.48:

briarroot \briarroot\ n.
   the hard woody root of the briar Erica arborea. [Also
   spelled brierroot.]
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

briarwood \briarwood\ n.
   wood from the hard woody root of the briar Erica arborea;
   used to make tobacco pipes.

   Syn: brierwood.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Brier \Bri"er\, n.
   1. the white heath Erica arborea. --RHUD.
      [PJC]

   2. a smoking pipe made of the root of the brier[1].

   Note: Brierroot seems to have been used formerly as a term
         meaning root of the Smilax laurifolia and is now
         defined as root of the Erica arborea. Not clear when
         this changed. -- PJC.
         [PJC]

The Collaborative International Dictionary of English v.0.48:

brierwood \bri"er*wood`\ n.
   1. wood from the hard woody root of the briar Erica
      arborea; it is used to make tobacco pipes. See also 2nd
      brier and brier root.

   Syn: briarwood.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Erica arborea
    n 1: evergreen treelike Mediterranean shrub having fragrant
         white flowers in large terminal panicles and hard woody
         roots used to make tobacco pipes [syn: tree heath,
         briar, brier, Erica arborea]