[ar.se.nic] n [ME, yellow orpiment, fr. MF & L; MF, fr. L arsenicum, fr. Gk arsenikon, arrhenikon, fr. Syr zarnig, of Iranian origin; akin to Av zaranya gold, Skt hari yellowish--more at yellow] (14c) 1: a trivalent and pentavalent solid poisonous element that is commonly metallic steel-gray, crystalline, and brittle
2: a poisonous trioxide of arsenic used esp. as an insecticide or weed killer--called also arsenic trioxide
[2]ar.sen.ic adj (1801): of, relating to, or containing arsenic esp. with a valence of five