trioxide : Idioms & Phrases
arsenic trioxide
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noun a white powdered poisonous trioxide of arsenic; used in manufacturing glass and as a pesticide (rat poison) and weed killer
arsenous oxide; arsenous anhydride; white arsenic; arsenic; ratsbane.
WordNet
Sulphur trioxide
(Chem.) , a white crystalline solid,SO3 , obtained by oxidation of sulphur dioxide. It dissolves in water with a hissing noise and the production of heat, forming sulphuric acid, and is employed as a dehydrating agent. Called alsosulphuric anhydride , and formerlysulphuric acid .