The Collaborative International Dictionary of English v.0.48:

Cudbear \Cud"bear`\ (k?d"b?r`), n. [Also cudbeard, corrupted
   fr. the name of Dr. Cuthbert Gordon, a Scotchman, who first
   brought it into notice.]
   1. A powder of a violet red color, difficult to moisten with
      water, used for making violet or purple dye. It is
      prepared from certain species of lichen, especially
      Lecanora tartarea. --Ure.
      [1913 Webster]

   2. (Bot.) A lichen (Lecanora tartarea), from which the
      powder is obtained.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cudbear
    n 1: a purplish dye obtained from orchil lichens [syn: orchil,
         archil, cudbear]