orpiment

noun

1. a mineral, arsenic trisulfide, As2S3, found usually in soft, yellow, foliated masses, used as a pigment.

noun

1. a yellow mineral consisting of arsenic trisulphide in monoclinic crystalline form occurring in association with realgar: it is an ore of arsenic. Formula: As 2 S 3

n.late 13c., from Old French orpiment “arsenic trisulphide, yellow color,” from Latin auripigmentum, from aurum “gold” (see aureate) + pigmentum “coloring matter, pigment, paint” (see pigment).