Main Entry: ¹ar·se·nic

Pronunciation: \ˈärs-nik, ˈär-sə-\

Function: 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