The Collaborative International Dictionary of English v.0.48:

Sandarach \San"da*rach\, Sandarac \San"da*rac\,, n. [L.
   sandaraca, Gr. ?.]
   1. (Min.) Realgar; red sulphide of arsenic. [Archaic]
      [1913 Webster]

   2. (Bot. Chem.) A white or yellow resin obtained from a
      Barbary tree (Callitris quadrivalvis or Thuya
      articulata), and pulverized for pounce; -- probably so
      called from a resemblance to the mineral.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sandarach
    n 1: a brittle and faintly aromatic translucent resin used in
         varnishes [syn: sandarac, sandarach]