What does "orpiment" mean?

Orpiment: Arsenic sesquisulphide, produced artificially as an amorphous lemonyellow 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. Our orpiment and sublimed mercurie. Chaucer. Red orpiment, realgar; the red sulphide of arsenic. -- Yellow orpiment, king's yellow.