arsenic

I. noun Etymology: Middle English arsenik orpiment, from Anglo-French & Latin; Anglo-French, from Latin arsenicum, from Greek arsenikon, arrhenikon, from Syriac zarnīg, of Iranian origin; akin to Avestan zaranya gold, Sanskrit hari yellowish — more at yellow Date: 14th century 1. a trivalent and pentavalent metalloid poisonous element that is commonly metallic steel gray, crystalline, and brittle and is used especially in wood preservatives, alloys, and semiconductors — see element table 2. a poisonous trioxide As2O3 or As4O6 of arsenic used especially as an insecticide or weed killer — called also arsenic trioxide II. adjective Date: 1801 of, relating to, or containing arsenic especially with a valence of five