Source : Webster's Revised Unabridged Dictionary (1913)

Brier \Bri"er\, Briar \Bri"ar\, n. [OE. brere, brer, AS.
   br[=e]r, br[ae]r; cf. Ir. briar prickle, thorn, brier, pin,
   Gael. preas bush, brier, W. prys, prysg.]
   1. A plant with a slender woody stem bearing stout prickles;
      especially, species of {Rosa}, {Rubus}, and {Smilax}.

   2. Fig.: Anything sharp or unpleasant to the feelings.

            The thorns and briers of reproof.     --Cowper.

   {Brier root}, the root of the southern {Smilax laurifolia}
      and {S. Walteri}; -- used for tobacco pipes.

   {Cat brier}, {Green brier}, several species of Smilax ({S.
      rotundifolia}, etc.)

   {Sweet brier} ({Rosa rubiginosa}). See {Sweetbrier}.

   {Yellow brier}, the {Rosa Eglantina}.

Source : WordNet®

brier
     n 1: tangled mass of prickly plants [syn: {brierpatch}, {brier
          patch}]
     2: a thorny stem or twig
     3: Eurasian rose with prickly stems and fragrant leaves and
        bright pink flowers followed by scarlet hips [syn: {sweetbrier},
         {sweetbriar}, {briar}, {eglantine}, {Rosa eglanteria}]
     4: a very prickly woody vine of the eastern United States
        growing in tangled masses having tough round stems with
        shiny leathery leaves and small greenish flowers followed
        by clusters of inedible shiny black berries [syn: {bullbrier},
         {greenbrier}, {catbrier}, {horse brier}, {horse-brier}, {briar},
         {Smilax rotundifolia}]
     5: 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}, {Erica
        arborea}]