The Collaborative International Dictionary of English v.0.48:

Orpiment \Or"pi*ment\, n. [F., fr. L. auripigmentum; aurum gold
   + pigmentum pigment. Cf. Aureate, Pigment, Orpin,
   Orpine.] (Chem.)
   Arsenic sesquisulphide, produced artificially as an amorphous
   lemon-yellow powder, and occurring naturally as a yellow
   crystalline mineral; -- formerly called auripigment. It is
   used in king's yellow, in white Indian fire, and in certain
   technical processes, as indigo printing.
   [1913 Webster]

         Our orpiment and sublimed mercurie.      --Chaucer.
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   Red orpiment, realgar; the red sulphide of arsenic.

   Yellow orpiment, king's yellow.
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The Collaborative International Dictionary of English v.0.48:

Auripigment \Au`ri*pig"ment\ ([add]`r[i^]*p[i^]g"ment), n.
   See Orpiment. [Obs.]
   [1913 Webster]