Source : Webster's Revised Unabridged Dictionary (1913)

Litmus \Lit"mus\, n. [D. lakmoes; lak lacker + moes a thick
   preparation of fruit, pap, prob. akin to E. meat: cf. G.
   lackmus. See {Lac} a resinous substance.] (Chem.)
   A dyestuff extracted from certain lichens ({Roccella
   tinctoria}, {Lecanora tartarea}, etc.), as a blue amorphous
   mass which consists of a compound of the alkaline carbonates
   with certain coloring matters related to orcin and orcein.

   Note: Litmus is used as a dye, and being turned red by acids
         and restored to its blue color by alkalies, is a common
         indicator or test for acidity and alkalinity.

   {Litmus paper} (Chem.), unsized paper saturated with blue or
      red litmus, -- used in testing for acids or alkalies.

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.

   2. (Bot.) A lichen ({Lecanora tartarea}), from which the
      powder is obtained.

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.

   2. (Bot.) A lichen ({Lecanora tartarea}), from which the
      powder is obtained.