WordNet sense 1 (a white powdered poisonous trioxide of arsenic; used in manufacturing glass and as a pesticide (rat poison) and weed killer):

ratsbane, arsenic trioxide, arsenous anhydride, arsenous oxide, white arsenic

WordNet sense 2 (a very poisonous metallic element that has three allotropic forms; arsenic and arsenic compounds are used as herbicides and insecticides and various alloys; found in arsenopyrite and orpiment and realgar):

as, as