The Collaborative International Dictionary of English v.0.48:

Lac \Lac\, n. [Per. lak; akin to Skr. l[=a]ksh[=a]: cf. F.
   lague, It. & NL. lacca. Cf. Lake a color, Lacquer,
   Litmus.]
   A resinous substance produced mainly on the banyan tree, but
   to some extent on other trees, by the Laccifer lacca
   (formerly Coccus lacca), a scale-shaped insect, the female
   of which fixes herself on the bark, and exudes from the
   margin of her body this resinous substance.
   [1913 Webster]

   Note: Stick-lac is the substance in its natural state,
         incrusting small twigs. When broken off, and the
         coloring matter partly removed, the granular residuum
         is called seed-lac. When melted, and reduced to a
         thin crust, it is called shell-lac or shellac. Lac
         is an important ingredient in sealing wax, dyes,
         varnishes, and lacquers.
         [1913 Webster]

   Ceylon lac, a resinous exudation of the tree Croton
      lacciferum, resembling lac.

   Lac dye, a scarlet dye obtained from stick-lac.

   Lac lake, the coloring matter of lac dye when precipitated
      from its solutions by alum.

   Mexican lac, an exudation of the tree Croton Draco.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lac dye
    n 1: scarlet dye like cochineal; extracted with alkali from
         stick lac