sulfur dioxiden. A colorless, extremely irritating gas or liquid, SO2, used in many industrial processes, especially in the manufacture of sulfuric acid, and as a preservative, disinfectant, and bleach. It is also a hazardous pollutant resulting from burning fossil fuels and refining sulfide-containing ores.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.sul?fur diox?ide n. a colorless, nonflammable, water-soluble, suffocating gas, SO2, formed when sulfur burns: used chiefly in the manufacture of chemicals such as sulfuric acid, in preserving fruits and vegetables, and in bleaching, disinfecting, and fumigating. [1865?70] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.sulfur dioxide A colorless, poisonous gas or liquid, SO2, that has a strong odor. It is formed naturally by volcanic activity, and is a waste gas produced by burning coal and oil and by many industrial processes, such as smelting. It is also a hazardous air pollutant and a major contributor to acid rain.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.